The secret is behind the "Coffee Shoppe" board in the bar. To open it, use the machine, then shoot the display (or press "use" on it) when "SLAM" appears.

Just outside the bar, there is a steel door above the ground; to reach the door, jump-run from the ledge containing electric pole and fans.

From the same ledge as in Secret 2, by going opposite way, along the catwalk, you get to a room locked from inside.

Just outside the bar, on the side of the concrete stairway, behind the big fan.

You can make your way inside the pharmacy by destroying part of the front wall; to do that, shoot the fire extinguisher through the window in the pink-lit back alley.

In the "Creamy Stick" shop there is a wall that can be destroyed, leading to a small office.

Across the street from the "Creamy Stick" there is a "Caco Bell" board that slides open.

High above "The Playful Noodle" there is a window leading to the buildings on the other side of the abyss. Getting to the window requires some effort. Start with a stool, jump onto the lamp, then on the metal roof. Next on the red neon arrow, then on the fan cage on the opposite wall. From there, relatively easily, to the fan cage just below the green one. The most tricky part is getting from there to the cables attached to the corner (second picture below). Then (third picture) to the cage just above the lower cable bridge, then on the cables, then on the higher cable bridge, cables again, then fan cage. From there you should be able to jump into the window.

The gauge panel slides down when used.

Behind the panel in Secret 1 there is a ladder leading to the top of the concrete column; from there, another panel can be reached (first picture). The area behind that is not itself a secret, but contains a switch marked with "?"; the switch opens similarly marked door in the red lit area near the maintenance corridor spider trap.

Near the Sit-Down-Little-Girl spider trap corridor, there is a blue container, stacked diagonally on a gray one. The easiest way to get inside is to use a trash bag to reach a ledge on the opposite wall, then jump around a pillar to the area with "SECTOR 06" neon, and run jump from there.

To make the jump for the armor on the column in the center of the main area, you need to start the fans (first picture) by walking over three pressure plates.

On the other side of the bridge leading to the blue door, there is a metal sheet that slides open.

The portable medikit can be reached by jumping out of the window between the two ducts.

The fan in the alley in front of "Bennet's Steam Letting CO" can be destroyed.
To get the boots in the "Bennet's Steam Letting CO" yard, you have to power up the big fan in the area that can be accessed by jumping from a ledge visible on picture 2 below.

To reach the red room, first you have to jump onto the side platform (visible on second picture), while being pushed through the wind tunnel. From there, jump to the higher platform on the opposite wall; then it's probably easier to jump to the ledge with the armor shards first rather than directly into the room.

There is a room hidden behind the metal grating.

Big fan in the final room can be destroyed with explosives.

The elevated area can be reached by jumping from the edge of the entrance tunnel.

There is a window in the wall of the concrete column facing away from the entrance tunnel.

The vent duct shielding on the upper floor (top elevator stop in the "Employees Only" area in the cafeteria) can be removed/destroyed.

From the same room as in Secret 3, through destroyed wall and orange container door you can get to a ladder leading down to a secret inside a green container.

From the landing point of the big fan-boosted leap, you can reach, by jumping around the pillar, the top of the column marked with a red circle. There is a switch, barely visible under a hologram. From there you can reach the top of the column with blue triangle, then the one with a yellow square, both with similar switches. Flipping all three, raises the bars blocking access to a secret with an armor and some bombs.

Swim underwater to get inside the crate floating in "Cannibals" cargo bay.

One of the pillars supporting the "Cannibals" logo is hollow. Jumping boots from Secret 10 greatly facilitate reaching the pillar.

In the office in the cargo bay, there is a minibar hidden behind a fake bookshelf.

High above the ground in the cargo bay there is a blue container; to get inside, you have to jump from the ledge on the outer side of the office window.

In the generator room there is a "Big Bill's Cars" ad covering entrance to a small chamber.

In the cafeteria, there is a wooden door controlled by three switches spread throughout the level. Switch labeled "0" is in the area at the bottom of the ladder in Secret 4. Switch "2" is in the elevated area in Secret 1, and switch "3" is in Secret 5, in the room behind bars. To open the door in the cafeteria, you have to flip the switches in sequence: "3", "0", then "2"; the on/off state of a switch doesn't matter, just the fact that the switch is used; the sequence can be restarted at any point, only the three most recent uses are taken into account. Also the door, once opened, will never close, regardless of any switch flipping.

You can open the dumpster in the corner of the plaza, by pressing "use" on the lid.

There is a secret apartment behind the mechanized door. To get inside, you have to power up two generator panels; first is in the corner next to the snack machine nearby; second is outside, behind some vines near the entrance to the plaza. There is a timeout -- in order for the door to open you must have both of the generators running at the same time.

The wooden barricade covering entrance to the old bathrooms can be destroyed with explosives.

In the hall with the monument, one of the columns slides open when used.

To unlock the service access door, use the switch in the reception.

Brick wall in the crew quarters can be destroyed with explosives.

In hangar, you can sneak through the bushes to get inside bay 5. There is a tank there. Use it's cannon to blast your way inside gate 1.

The elevated area next to the landing pad is a secret. One way to get there is to use the jumping boots from Secret 5.

To access this secret, you have to open one of the red bulk doors in the pit under the main entrance to the base. Switches controlling the door are located next to the turrets on balconies overseeing the lot.

The glass column in the center of the rotunda opens when used.

You can climb inside the screen beam in the main hall, using a chair (for example). Two of the four panels at the top lead to secret areas.

There is a secret behind a grill in the target dummy course. Probably the easiest way to get to the sloped area is to jump from the nearby brick window.

In the robot hangar, there are two generator panels hidden behind computer racks at opposite sides of the central wall. Activating both generators opens a secret.

In the core control room there is a vent duct leading to a secret area.

There is an armor on the catwalk in one of the rooms adjacent to the service station.

In the service station, near the second elevator, there is a crawlspace; use the lever switch to gain access to it.

Through the service station control room, you can get to the abandoned part of the base. Immediately behind the door, there is a small bridge. If you look up from there, you will see a duct covered by a metal grate in the ceiling; shoot the grate and a ladder will drop.

In abandoned part of the base, you can get to the red lit room through the broken window, with a help of a chair, for example.

The switch in Secret 4 in addition to opening the door immediately next to it, also lifts the door to the office at the opposite end of the bridge a bit.

There is a portable medikit at the top of the destroyed wall.

There are two secret areas in the destroyed building; you can get to the first by jumping on the exposed support beams. The secret is at the top of the slope.

To get to the second secret in the destroyed building, instead of on the support beams, jump on the concrete slope. The transparent wall at the end of it is fake -- you can just jump inside the room.

This secret requires some tricky jumping. From the red car wreck, take the ladder to the top of the lamp post. From there, jump to the platform shown on the second picture; then you will be able to reach the ladder on the next lamp post, and from the top of that, the final platform. Use the switch on the light control panel to drop the ladder that leads to the secret. The cake at the top is a lie, and the bowling bomb likes you more than the companion cube.

Near the location when the red card is found there is a destructible door.

There is a hole in the ceiling above the hanging lamp in the escalator area.

In Secret 2 there is a large hole in the wall at the top of the slope. Throwing a bowling bomb inside will cause a large explosion which will remove a chunk of rubble below, near the exposed steel beams. Walk through the opening to get to this zone's mega secret.

A dustbin and a trash bag mask an entrance to a vent duct leading inside the "Color Code" store.

Dive into the fountain to get to some goodies.

Breaking the tank of the water stand exposes an armor.

The black-white picture, next to the "Information" board, slides open when used.

There is an entrance to a small cave hidden in the grass.

In the surveillance room, the screen showing Guru Meditation opens when used.

In the underground lot, in the crack at the spot where the truck hit the wall, there is a switch; shooting it opens the truck's trailer.

Blasting the projector screen (together with the wall behind it) in the lecture room opens access to the elevated yard next to the entrance to the underground lot. From the yard, you can reach the small ladder on the fan box, and jump to the other side. The secret area is behind an illusionary wall on the second floor (location shown on the third picture). To get there, you have to power up the fan -- the generator panel is inside the fenced area. Without jumping, allow the fan to lift you as high as possible, then just move towards the wall.

The wall next to the "Dr. Angelo" ad is illusionary. You can reach the area behind it by jumping from the top off "No spine -- No problem" board.

There is a secret inside the fireplace in the conference room.

The maintenance access leads to a secret area.

In the ventilation duct connecting the conference room and the showroom, there is a sloped section where the duct panelling has slightly different color; that part of the wall is illusionary and leads to the garden.

You can get inside the barred bathroom through the vent.

In the room with a big marble column in the center, approaching the picture of a pine forest opens a secret area at the base of the column.

In the employee-only area, entering the bathroom lowers one of the lockers.

In the kitchen, there is a secret area under the refrigerator.

In the other part of employee-only area, there is a room with a wall of green panels. Use a switch on the panel with a screen, to uncover entrance to the maintenance tunnel.

Deeper into the employee-only area, behind pink sliding door, there is a small dim-lit room; behind the panel box, in the part covered by shadow, there is a drop allowing you to crawl underneath the box.

In the room with glass fountain, there is a secret door in the wall, opened by a brick.

From the bathroom adjacent to the glass fountain room, you can get to the area behind locked glass door. To do that, you have to jump from the broken bathroom window onto a fan cage, and to the secret area directly from there. Note that there is an autosave point in the bathroom, so you can jump and fail freely.

In the 6502 presentation room, pushing the red book opens access to a secret area behind the fireplace.

There is a secret area at the top of the round panel column.

In the dead end corridor, where blue card is located, there is a stack of hollow brown boxes.

In the same area as Secret 2, using the laptop displaying "Piano tutor 1.4" opens one of the wooden crates.

Back In the locker room, one of the lockers has slightly different color. To open it, you have to jump on the top of it. Inside, there is a piece of decorative rope; pulling it opens access to a switch in the nearby room; the switch in turn opens a manhole in the area behind the door unlocked by the blue key card. The secret area, in addition to an armor, contains the solution to the piano puzzle found later in the game.

In the piston pit, there is a secret at the base of the concrete pillar.

Accessing the terminal aimed at the rotating glass cube, causes an explosion destroying part of the computer rack; that allows you to climb to the secret area at the top.

Tight passage between racks leads to another secret area.

The darker part of the metal wall slides open when used.

In a vent duct in the area with plasma beams, there is a vertical section with a fan and a switch at the bottom. The switch opens access to another section of the vent.

At the location where the yellow card is found, there is a secret in the wall above the computer screens.

In lab, there is a desk with a surveillance monitor and two computers. Pressing use on the one on the right opens a secret area.

After the power grid has been blown up, the reactor room becomes accessible. There is a secret in a vent there.

Crawling under Heskel's desk (yes, Alyx, it's like a "hesk") lowers the floor to reveal a secret area there.

In the penthouse pool there is a small cave behind the damaged wall.

Next to the penthouse office, there is a wall section that opens; you can reach it by jumping on flower boxes outside the office windows.

To get the purple key card, play "D C A D C F" on the piano; timing does not matter. The "A" and the "F" must be the ones below the "C".

A door with a smashed button blocks entry to a bathroom. One way to get to the bathroom is to jump around the wall, into the bathroom window, off the right corner of the window next to the piano.

In the corner of the room with self-destruct button, there is a secret below the piston.

Near the bottom stop of the elevator that carried you of the exploding laboratory, you will find a door that requires the purple key card to open. If you have picked up the card in Secret 4, you can use it here to gain access to the secret "Grand Slam" level.

There is a secret in the vent just next to the entry point to the level.

In the bar, below the "McMonster" poster, there is a vent access; inside, part of the duct paneling with red speckles on it, can be smashed, opening way to a secret area.

On the second floor, you can reach the secret area inside the broken elevator through the ventilation duct; make a hole in the wall around the corner to get into the vent.

The bench, in front of the "employee-only" door on the second floor, slides sideways when used.

There is a secret area at the top of the stadium display. You can reach the ladder with a help of jumping boots, of which there is quite plenty in this level.

Walk back from the starting point, through the door to the back of the train -- there is an armor there.

There is a secret area inside red container with "Doomed" graffiti.

The second freight car (counting from the lab car) carries a steel crate that slides sideways, revealing an armor.

Front wall of the derailed train car can be destroyed with explosives.

Jumping on the top of the thin black container (the one with no "NOTICE") opens a fake brick wall.

Shooting fire extinguisher in the main hall creates a way around the exit gate. Be quick if you want to collect the bombs and clusterpucks also -- when you step out of the hole, the ceiling on far end of the corridor starts to cave in.

In the snack shop, using the cash register lowers the nearby shelf.

Hitting a bullseye with a dart reveals a secret.

In the lounge, in the wall opposite to the door to the manager's office, part of wooden paneling slides sideways when used.

In the archive room, there is a no-smoking sign; pressing "use" on it reveals a secret behind the wall of file cabinets.

In the manager's office, in the room behind glass walls, there is a button labeled A3-5 on the left side of the keyboard panel. The button opens a bulk door in the part of the level behind yellow card door. The secret area behind that door is flooded with radiation, which drains your health really fast -- a girl is going to need some extra protection in order to survive. A protective suit can be found in the part of the station further down the rails, near the point where you pick up the yellow key card; there is a train car with a square hole in the roof; the suit is inside.

In the room at the very beginning of the level, there is a secret area behind the blue section of the wall.

In flooded monorail track area, there is a crack in the wall, barely visible above the water surface; shoot the crack with explosive weapon to reveal a secret.

On one end of a bridge above the monorail turntable, there is a door obstructed with a crate. The room behind it is a secret area. You can get on the bridge through a vent.

You can use a vent duct nearby to get to the room below the track.

Swim underwater in the monorail gate B to get to a secret area with some items on a floating plank.

The flooded area behind gate A is a secret. You have to cycle the gate first to get there -- the control lever has to be in the upper position.

On the monorail station, there is a corroded green container on the upper platform, near the elevator. The container can be blasted open with explosives; aim at the crack near the top.

On the monorail station, in the corridor leading from the elevator to the track control room, there is a striped metal plate that reveals a button when used. The button opens a secret area.

In the control room, there is a switch on the back of the computer rack.

On the lower platform of the monorail station, the whole area above the red-white stripe signs is a secret (orange container with a "Funk You" graffiti occupies most of it). The easiest way to reach it is to jump from the window of the control room.

On the way out of the station, there is a crack in the rock beside the track. The cave behind it is a secret area.

Walking down the rocky tunnel, leading from the station to the monorail bridge, triggers an explosion that makes another entrance to the cave with green goo lakes. In previously unreachable part of the cave, there is a spot with a piece of broken ladder and few red barrels. There is also a concrete wall with a square hole in it, leading to a secret area.

The explosion mentioned in description of Secret 12 also destroys a section of a red pipe. By diving into the pipe you get to another secret area.

You have to break the grate and swim below the track to reach the clusterpucks.

The grate near the small turntable slides open when used.

Going through the door at the platform near the barricaded tunnel, you get into a long corridor; there, in the wall next to a blue pipe, just above the floor, there is an entrance to a secret area, where uncle Frank waits for you guarding a switch essential in getting into Secret 4.

At the other end of the barricaded tunnel, there is a railway car; unless you have already flipped the uncle Frank's switch in Secret 3, the car blocks access to a creepy secret room here.

Inside the big water tank, on the railing above spiral stairway, there is an armor. The jumping boots respawning nearby greatly help in reaching the armor.

At the bottom of the water tank there is a side corridor containing chaingun ammo and an ultrasonic radar. You have to swim close to the wall to overcome the opposing current.

In the control room adjacent to the big water tank, in the corner behind cylinder marked "GATE A", there is a wall section that opens.

In the coolant control room, using green screen panel opens a secret.

In the hall with three giant pistons, there is a part of floor paneling that sticks out; this is a pressure plate, opening nearby vent. Inside, there are two section where the vent is wider. In the one farther from the entry point, a part of the vent wall can be destroyed.

Back at the station where monorail track ends, there is a secret that becomes easily available on your second visit there, after the lockdown has been lifted.

At the low end of the tracks, near the entry point to the level, there is a destructible brick wall.

The classic secret behind waterfall is here. If you look closely, there is a barely visible line on the wall of water, giving a hint where the platform is.

At the back of the inn, in the dark room with a sink and a food tray, there is a blue file cabinet that slides into the floor when you climb onto it.

Adjacent to hospital waiting room there is a small room with a surveillance monitor and a panel with a switch that opens secret door at the other side of the wall. Standing in the waiting room near the secret door, you can shoot the button through a hole left by exploding fire extinguisher.

In the maintenance room in the hospital, above a stack of medical supplies, there is a vent access that leads to a secret area.

In the upper hospital room, there is a poster with piano keyboard and prosthetic hand; pressing "use" on the poster opens secret area in the opposite wall.

The tunnel behind the destroyed railway bridge (the steel one, on the other side of the hospital) is a secret area. You can get there easily using jump boots that respawn just below.

In the upper part of the sewers, there is a spot with a pile of mud bursting through the wall; a grate near by opens to a secret.

There is a vent just next to the grate in Secret 1. Inside the vent, you have to beat your way through the paneling to reach the room behind a strange semi-transparent plastic sheet.

Standing at the junction in the corridor connecting blue keycard door and a bulk door labeled "employees only", and looking above the railing, you will see a metal ledge covered by some vines. You can reach it by jumping from a concrete pillar. Following the ledge to the right gets you to a secret area.

Back wall of the safe opens to a secret.

If you follow the green pipe to a dark, narrow room, not far from "GATE A" door, you will notice a crack in the wall. Shoot it with explosives to uncover an entrance to ninja hideout.

After swimming through newly opened gate B, follow the current and on the last junction take your left instead of swimming straight into the main reservoir. Going up the ladder and jumping out of the pipe you end up in dimly lit hall with lots of small pipes covering the floor. On the other side of a sheet metal walkway there is a similar hall with two large pipe access holes (third picture). The one on the left contains a secret area; the grating on it is vulnerable to explosives.

On the other side of the wall from the section with three large fans in the floor, there is a vent access; inside the vent, opposite of the small window covered by a grate, a bit above the duct floor, there is an illusionary wall leading to a secret area.

Near the gate A control wheel, the wall with biohazard warning sign is illusionary. It's not reachable directly from the floor, so you are going to need a boost (there is a broom near by) or jump from the railing.

To get to the heavy armor on the beam just below the ceiling, after jumping down into the blue pipe, search the wall on your right for a secret door. The fan behind it will lift you to the tunnel that leads to the armor. Warning -- picking it up opens a door with a spider surprise.

Near the elevator that takes you to a platform where the pink control valve is, there is a small tunnel with a secret door.

At the top of a long ladder in water treatment, in dark corridor where you encounter a mutant, there is a panel that slides down when used, revealing a vent access to a secret area flooded in blue light.

On the bottom floor of the house, there is a wooden secret door behind stack of boxes.

Next to the bathroom, there is a curtain and a drapery cord beside it. Pull the cord to open a secret area.

In the dining room, there is a peephole disguised with a portrait of Heskel. To get to the room behind it, press "use" on the wooden cabinet in the foyer.

In the small office upstairs from the library, the wall behind the picture of a skull is illusionary.

In the balcony in the library, near the door to the manager's office, there is a secret passage behind the picture of a madonna sculpture.

The basement accessible from the yard is a secret area.

In the lower level of the crypt, after solving the red key card puzzle, you gain access to the crawlspace filled with water. There are four grates in the crawlspace; the one that is the farthest from the "manual override" switch, can be opened, revealing a secret area.

If you drop a few lit bowling bombs down the chimney of the building in the center of the yard, the interior of the building becomes accessible; dive into the fountain to get to the passage that leads there.

In a small room to the left from the corridor leading to the manager's office, there is a tree painting that covers a secret tunnel.

Shoot the moon down to score the zone's mega secret.

Gray metal plate near a big "ATTENTION" sign slides sideways when used.

In the room with zombies in four closets, there are two stacked blue containers. The bottom one contains a secret.

Just behind the door leading out of the zombie closet room, there is a vent access leading to a secret area.

At the top of the ladder, in the purple brick hall, there is a row of five lockers, and a vent access above it. Inside the vent there is another grating you have to open to reach a secret area.

If you head in the direction away from the lockers, you will reach a gray brick room with water dripping from the ceiling. Jump over the fence there an swim underwater into a short corridor with a switch-operated door as it's end. In the room behind it, swim back to the surface to find another secret area.

Adjacent to the rocky room there is a room with a mirror; the mirror has a secret behind it.

On the bridge with a turret, at the beginning of the level, if you swim underwater you will find an armor in the opening in the floor.

From the junction next to the turret bridge, head forward towards the bulk door, then jump over the railing and follow the pipe to a hole in wire fence. If you go through the hole and head left, you will find a secret area (you may want to get the protective suit from Secret 3 first).

In the goo mixing vessel there is a wooden panel that is vulnerable to explosives. In the secret area behind it you will find a protective suit, mighty useful in all the goo excursions in this level.

In the hall with six tanks filled with greenish goo, there is a secret area below the floor; you will have to take a quick bath in the liquid to reach it. If the girl is doing this without protection, it will actually hurt less if you submerge completely. It's not hard to get in and out of the secret with losing 5 HP or less in total.

The wall above the computer rack is illusionary.

In the room behind a purple garage door, there is a broken screen that opens when used.

Next to the ambush room, there is a corridor with a stack of boxes blocking the way. There is a secret area behind the boxes.

In the showroom with exoskeletons, the fire alarm switch opens a secret.

This secret is located in the part of the level that becomes accessible on your second visit there, after completing the "Parting Procedure" level, in which case you will be arriving in this level via an elevator.
Adjacent to the crane room, there is a small room with gray panels on the wall opposite to the door. Press "use" on the bottom-right corner of the panel to open a tunnel leading to a secret area.

Behind the second laser gate there are double doors with lots of padlocks on them. You can get into the room behind through a vent duct just next to the door (you may have to blow up the cabinet to access the duct first).

In the corridor near the room where the cyborg holding yellow key card is assembled, there is a steel gate that becomes non-solid once you have completed all tasks in "Parting Procedure" level. Walk through the gate to find the mega secret.

In the first biodome, there is a stack of boxes which you can use to reach the ceiling and break through the cooling fan to get to the crawlspace above. Regardless of which direction you choose there, you will reach the green part, behind transparent sheets of plastic. On the rear side of the central column there is a switch that opens a secret.

There are jumping boots under the water on the left side of the drawbridge.

Under the water near the rotating columns, just below the surface, there is an entrance to a flooded tunnel that leads to a secret area.

In the bathroom at the other end of the sector B biodome, press "use" on the door safety poster to open a secret in a wall above the stalls.

In the room behind the decontamination chamber, near the location where you pick up the blue key card, there is a wall with warning signs on it. Press "use" on the one on the left to open a secret area behind a computer rack on the opposite side of the room.

In the biodome in sector B, go through the broken window. Past the goo lakes, there is a small waterfall flowing into a flooded cave; if you swim to the other end of the cave, you will find yourself on the other side of the biodome; there is a tree stump near by, and a narrow tunnel just above it; the tunnel leads to a secret area.

At the far end of the corridor with zombies in vats, there is a crack in the wall above the corrosive warning sign in mini chem lab.

To access this secret, first you have to retrieve the red key card, so that and the area on the left side of the corridor in biodome C becomes accessible through a broken window. The secret is in a small cave halfway through the tunnel connecting two goo lakes.

Near the location of Secret 8, there is a vent access covered by some vines. This one won't budge and you have to destroy it. The secret area is at the rear end of the water tank.

In the cave near the end of the level, there is a hidden vent access in the wall above the mine cart.

In the cave at the beginning of the level, there is a column of goo flowing from the ceiling. The column is non-solid and you can swim inside it just like in a regular goo lake. Swimming all the way up teleports you to a small island under a rather depressing acidic-green sky. Grabbing the armor shard teleports you back into the cave; from there, you can jump into the slime column again, and again after that, ending up on islands with stones containing varying inscriptions. The one you get to after the "door unlocked" message appears on screen, seems to be the final one.