Due to the sheer randomness in the expansion (Temple of the Sun) regarding the secrets, i can not cover them all. The secrets in this guide are by far not all of them, so if you find a secret that has not been covered here, and by chance have the pictures (ingame and map), then please do share.
Either way, nearly all secrets are rather easy to spot, so just stay cautious and you´ll be fine!

This guide contains major spoilers! It is possible to play the game while just viewing the information of the floor you are currently in. Thats why every section of this guide is its own floor. If there are secrets in other sections of the floor, which are only reachable by passing through other floors, there will be a line inside that section.
Scipping forward will reveal upcoming enemies, landscapes and traps. Please bear that in mind while reading.

All secrets have been covered, so if there is a room, stairs or anything you can not reach in a floor, you are not able to do so. There are some regions you are not allowed to enter, until later in the game.

• hipshot
  
• Chief
  
• Snaeng
  
• riz -bt-
  
• Jermurzu

• BW: Breakable Wall (A wall you have to hit to make it disappear)
  
• IV: Invisible (A wall you can simply walk through)
  
• ST: Switch (A switch you have to trigger)

Every single secret in this guide is built in this order:

[Shortcut of the type] Number of the secret:
Short description where it can be found.
What you will gain from finding it.
Ingame picture showing the secret ; Ingame picture showing the location on the map

The ingame picture is always BEFORE revealing the secret, while the picture of the map is always AFTER revealing it!

Just looking for the planks? They are marked in big letters in every section. Here is a quick list about which secret in which section contains the plank:

Floor 1: Secret 3
Floor 2: Secret 7
Floor 3: Secret 6
Floor 4: See floor 6!
Floor 5: Secret 2
Floor 6: Secret 1; Secret 2
Floor 7: Secret 4
Floor 8: Secret 2, Secret 4
Floor 9: See floor 8!
Floor 10: Secret 1
Floor 11: Secret 5
Floor 12: Secret 1

Just looking for the achievements? Here is a quick list about which secret in which section contains the achievement:

Harvesting: Floor 3, Secret 7
The Heist: Floor 4, Secret 5
The Grisly Combination: Floor 6, Secret 1
Earth & Void: Floor 8, Secret 6
Midway: Floor 10, Secret 2
Doomed Space Marine: Floor 12, Secret 5
Desert Zone: Temple Floor 1, Secret 2
Do it like Jones: Temple Floor 2, Secret 3
Serious Pickup: Outside, Secret 1
Daniel the Traveler: Outside, Secret 1
Pyramid of Fear: Outside, Secret 1

Warning!: This will spoil the content of the easter eggs.

Harvesting:
Command & Conquer. The picture represents Tiberium, which has to be harvested to gather resources.
The Heist:
Payday: The Heist. The picture represents Wolf´s mask on the floor, which he lost in "First World Bank" (the promo level).
Earth & Void:
Civilization 1. The picture represents a city of size 19. The text is from it´s intro.
Doomed Space Marine:
Duke Nukem 3D. This is an easter egg in Duke Nukem itself, referring to Doom. The text is, what Duke says, finding the spacemarine.

2015-11-10 : Updated Hall of Fame
2015-03-27 : Switched to international dates
2015-01-11 : Miinor improvements.
2014-10-18 : Minor improvements.
2014-10-17 : Added some secrets. Added reminder.
2014-10-02 : Gathering information regarding expansion. Updating a few screenshots.
2014-10-01 : Updated to include the expansion.
2014-05-27 : Fixed some minor errors i made.
2014-05-23 : Removed the note that there may be secrets missing. Removed "Riddle" from the
shortcut log. Made the names of the hall of Fame section into links to the
corresponding players profile.
2014-09-26 : Clarity improvements
2014-04-16 : Minor Improvements
2014-02-03 : Added "Midway" and "The Grisly Combination" achievement
2013-12-19 : Updated challenge section
2013-12-18 : Added floor 3 3/4 again... yay
2013-12-17 : Updated the guide to be accurate to patch 1.2
2013-12-02 : Fixed a bit of my horrible english
2013-11-13 : Minor improvements
2013-10-19 : Changed the order of the secrets a bit to be more accurate. Added the secret on the
Queen´s floor.
2013-08-24 : Minor improvements. The guide is now spoiler free.
2013-08-23 : Minor improvements. Guide should be finished now. Added The End section.
2013-08-22 : Added challenge section and hall of fame.
2013-08-22 : Deleted solving of riddles. Finally added the secret at the start of the game (floor 10),
Added the last achievement, added a spoiler tag for 2 pictures.
2013-08-22 : Added achievement explanation. Added some secrets. Added Special Thanks
section.
2013-08-22 : Achievements updated. Minor improvements. Last achievement will come soon.
2013-08-22 : Act IV completed. Minor improvements. Guide up to date.
2013-08-21 : Act III completed. Added achievement-finder.
2013-08-21 : Act II completed. Minor improvements.
2013-08-21 : Guide goes public with act I. Will soon be updated!

[BW] Secret 1:
Northern side of the map, before picking up the first bronze key.
A few coins and a health potion!

[BW] Secret 2:
Behind the bronze door, right before crossing the bridge, on the left side.
Coins and a gold coin!

West of secret 2.
A portal to floor 3! This leads to missing the plank on floor 2, so only use this if you want to get somewhere really quick!

[IV] Secret 3:
On the right side of the map, before crossing the two bridges to the north.
A strange plank!

[ST] Secret 1:
On the bottom left side of the golden door.
A few coins.

[IV] Secret 2:
Top left of the map, behind the spike riddle.
Coins and a gold coin!

[BW] Secret 3:
Top right corner of the map where you find the golden key.
Coins and a random reward!

[ST] Secret 4:
Activate 4 runes nearby the area south of the golden door. All but one rune are behind bronze doors to which the keys can be found closely by.
A gold coin and a chest!

[BW] Secret 5:
On the left side after crossing the giant wooden bridge.
Spawns a chest into secret 7!

[BW] Secret 6:
On the left side of secret 5.
Opens Secret 7!

[ST] Secret 7:
On the left side of the giant bridge, go up, then left. You can see the plank floating. You need the switch of secret 6.
Coins, a strange plank and a chest (after activation of secret 5)!

[BW] Secret 8:
Top left before goin through the golden door.
Riddle. Gives 1 life (a little bit south)!

[ST] Secret 1:
North of the entrance.
Secret shop!

[BW] Secret 2:
West of secret 1.
A few coins and a gold coin (a bit south).

[ST] Secret 3:
In the center, east of the defense shop. Can be entered after activating 5 switches (see pictures below).
A riddle. You gain access to the bonus level, containing a potion, a heck load of coins and a life!
Here the location of the 5 switches:


How to solve this puzzle quickly:
The puzzle looks like this:

Step 1:

Step 2:

Step 3:


[BW] Secret 4:
South of the checkpoint bottom right corner of the map.
Coins and a shop!

[BW] Secret 5:
Just east from the checkpoint in the spikes, deactivated a bit south.
Coins and a shop!

[BW] Secret 6:
You need to activate two switches for this to open. The first one is in the bottom left corner of the map, where the bats were. That switch opens another passage, south of secret 5 near the spike trap (for pictures see below). Finally the last passage south of the boss door opens.
A strange plank!

Here the location of the switches:

[BW] Secret 7:
Inside the last passage of secret 6.
Coins and the achievement "Harvesting"!

[--]Secret 1:
Behind the teleporter to enter the bossfight.
A golden coin!

From the second act on, the walls you have to break are not visible anymore (they had cracks in the first act). In the following pictures, the wall has already been hit once, so you can see exactly, where the part of the wall is. They do not look like this before hitting!

[ST] Secret 1:
East, just to the right of the room with the bajillion skelettons and the bronze door. The switch opens up a room with a riddle a bit to the north. This opens a passage inside the room with the scelattons.
A life, coins, 2 chests and a golden coin!

[ST] Secret 2:
A bit north of the east area (after entering floor 4) in the passage with the grid. Opens a room a bit to the north.
Coins and a gold coin!

[IV] Secret 3:
Just to the right of secret 2.
A life!

[BW] Secret 4:
East of the boss switch.
A random reward!

-----------------------------------------After Floor 6, Secret 1----------------------------------------------

[BW] Secret 5:
After floor 6 secret 1, you can go over the magical bridge to floor 5. From there, go to the south of this area and take another staircase down to floor 4.
You will find a strange plank there. Break the wall in the north to get this secret.
Coins and the achievement "The Heist"!

[BW] Secret 1:
On the right side of the only silver door there is in that floor.
Coins and a random reward!

[BW] Secret 2:
On the right side of the map, where you can see the plank floating through the wall.
A strange plank!

[IV] Secret 3:
Top right corner of the map, behind a bronze door.
A riddle. A life!

--------------------------------------------From floor 6 with secret 1-------------------------------------------------

[ST] Secret 3:
Right as you enter, on the right side. You need to activate a switch for the portal, which can be found north of the pyramid where the plank is.
Entrance to the bonus level. There (top left corner) you can deactivate the blue spikes on the right, to get more coins and a life!

[ST] Secret 1:
As you go to the north, you eventually have to turn east to get into a room with 5 switches located between spike traps. After their activation, 2 passages (and enemies) will appear closely by. In each passage is another switch.
Don´t forget to collect the strange plank in floor 4! You can reach it by taking another staircase in the south of floor 5. Also take floor 4, secret 5 with you once your there!
2 strange planks, the bonus level, many coins and the achievement "The Grisly Combination"!

[ST] Secret 2:
The plank will be at that location after you hit the switch in floor 5 (picture below). You can reach that switch with secret 1.
A strange plank!
Here the location of the switch in floor 5:


[BW] Secret 3:
Right after the room with the spike traps and the switches for secret 1.
Coins, a chest and a shop!

[IV] Secret 4:
East of the entrance to floor 6, west of the huge room with the spike traps.
A life!

[ST] Secret 1:
Behind the first silver door. The key is behind the bronze door, and that key is in front of it.
A chest!

[ST] Secret 2:
Right after secret 1, going further north there is a switch in the way.
A few coins in a room a bit south.

[IV] Secret 3:
At the top center of the map, right after the second checkpoint.
Coins and a random reward!

[ST] Secret 4:
At the center of the map. You have to activate a switch to get to it (picture below). It´s near the Shop in the west.
A strange Plank!
Here the location of the switch:

[IV] Secret 1:
In the southern area, left of the spike traps which lead to the plank.
Reveals the way to the plank!

[ST] Secret 2:
Activate the switch from secret 1. The path is south of you.
Coins, 2 chests and a strange plank!

[BW] Secret 3:
To be able to break this wall, you need to activate the switch between the 2 chests of secret 2.
A riddle. Gives a random reward and coins in a room appearing north of you!

-------------------------------------After the bonus level in floor 9 (secret 8)-------------------------------------

[--] Secret 4:
After the bonus level, you spawn near the stairs down to floor 8. Once there, just go south.
A strange plank!

[ST] Secret 5:
Just hit the switch next to the stairs to open the passage west of you.
2 chests, coins and a life!

[BW] Secret 6:
In the passage of secret 5.
Some coins and the achievement "Eartch & Void"!

[IV] Secret 1:
In the center, where you can find the golden key, right next to it. The life will be there if u hit the switch on the other side of the wall (to the right, visible on the picture).
A life!

[ST] Secret 2:
On the bottom left side, where the giant bronze door is. Behind the door on the right side is a switch.
2 chests.

[BW] Secret 3:
On the left side of the giant bronze door and secret 2.
A switch, revealing a room (north) with coins and more secrets.

[BW] Secret 4:
Inside the hidden room of secret 3.
Coins, a chest and more secrets.

[BW] Secret 5:
Inside the passage of secret 4.
A chest, coins and a gold coin!
Switchorder: The one next to the chest to deactivate the spikes near you, the one on the spikes, the one in the passage which just opened.

[IV] Secret 6:
In the area south of the 2 shops with silver doors.
A gold coin!

[BW] Secret 7:
In the flamefiled, near one of the switches for secret 8.
Coins, a gold coin and one switch for secret 8.

[ST] Secret 8:
You have to hit 5 switches in the area (pictures below) to get here.
Opens up a riddle. Just click the symbols you have to, to reveal a passage in the west to the potal. You can enter the bonus level, containing Coins, a potion and a life!
Here the location of the 5 switches:

-------------------------------------After returning from the bonus level-----------------------------------------
[--] Secret 9:
After the bonus level from secret 8, move south until you reach the end with a riddle which makes the bridge appear.
5 lifes!

Funfact:
You can crush this wall (even from the top) to shorten your way through the dungeon.

[--] Secret 1:
The plank is to the right of the flame turret (which can be disabled by a switch near by at the right walkway). You can reach it by entering the portal in the south (picture below).
A strange plank!
Here the location of the portal:


[ST] Secret 2:
North of the portal seen in secret 1. Behind the portal of secret 1 is a switch (activated as if you wanted to enter the portal from the top).
A random reward and the achievement "Midway"!

[ST] Secret 1:
After activating the switch in the boss-portal room, go south.
A random reward!
Here the loctaion of the switch:


[IV] Secret 2:
Top left side of the map, in the spiketrap-field.
A riddle. You get 2 chests, a golden coin and a life!

--------------------------------------------After returning from floor 12--------------------------------------------

[ST] Secret 3:
Hit the swith inbetween the portals from floor 12 secret 2 (pictures below).
2 Shops!

[ST] Secret 4:
You have to activate 5 swtiches for this to open (pictures below). It is a riddle in the center of the area.
A riddle. You get entrance to the last bonus level!
Here the location of the 5 switches:


[--] Secret 5:
In the center of the bonus level.
The last strange plank!

[--] Secret 1:
On the top left corner of the map, where all the orb shooting enemies are (you can go west and trigger the spike trap there. It will kill all turrets).
A strange plank!

[ST] Secret 2:
You have to activate 6 runes (pictures below). Then a path to a portal will open in the bottom left corner of the map.
A chest, a secret in floor 11, a life and a way to secret 3!

Here the location of the 6 runes:

[IV] Secret 3:
In the revealed passage of secret 2.
Opens the switch for secret 4!

[ST] Secret 4:
After secret 3, you can activate a switch (picture see below).
2 chests, 5 lifes and a way to secret 5!
Here the location of the switch:


[BW] Secret 5:
In secret 4.
Coins and the achievement "Doomed Space Marine"!

Keep in mind that all of these secrets are randomly generated. They may or may not appear and the rewards may or may not differ from those listed here.

[BW] Secret 1:
South of the broken bridge.
A life!

[BW] Secret 2:
North of the broken Bridge.
A random reward!

[BW] Secret 3:
Inside secret 1.
Some coins!

[BW] Secret 3:
West of secret 1.
Some coins!

Keep in mind that all of these secrets are randomly generated. They may or may not appear and the rewards may or may not differ from those listed here.

[BW] Secret 1:
Between the level entrance and the teleporter to the left.
Some coins (or a life)!

[BW] Secret 2:
North of the teleporter. Does not have to appear.
A life!

[BW] Secret 3:
South of the repaired bridge below the checkpoint.
A life!

[BW] Secret 4:
South of secret 3.
A random reward!

[BW] Secret 5:
Northwest of the exit (entrance already destroyed in picture).
Raises the bridge to get the ore (east)!

Keep in mind that all of these secrets are randomly generated. They may or may not appear and the rewards may or may not differ from those listed here.

[BW] Secret 1:
In the nothern part before the giant bridge.
A random reward!

[BW] Secret 2:
Inside secret 2.
Some coins!


[BW] Secret 3:
In the nothern part after the giant bridge.
Some coins!

[BW] Secret 4:
If you got there secret in the northern area after the giant bridge, this secret may appear inside it.
Coins and a life!


[BW] Secret 5:
East of the giant bridge.
Some coins!

[BW] Secret 1:
After the bossfight, going back to the deactivated bridge.
A life!

The passage is randomly generated and some areas have one (or for the most part more) secrets, and some don´t.
Just keep a lookout on the northern walls for cracks...

Keep in mind that all of these secrets are randomly generated. They may or may not appear and the rewards may or may not differ from those listed here.

[BW] Secret 1:
East of the exit.
A random reward!

In the southeast corner you can also get the "Desert Zone" achievement, activating the switch after the mana draining passage and falling into the revealed hole. For further information on this, check this

Keep in mind that all of these secrets are randomly generated. They may or may not appear and the rewards may or may not differ from those listed here.

[BW] Secret 1:
Southwest, next to the teleporter.
A random reward!

[BW] Secret 2:
To the right of the huge flame field in the next big room.
A random reward!

[BW] Secret 3:
North of one of the sunlight pillars above the checkpoint.
A random reward!

[BW] Secret 4:
North of the entrance. Note: Behind the portal is a switch making the mana upgrade accessable.
A 6 lifes, a health upgrade, a lot of coins, one of the six pyramids and a mana upgrade!

Here the location of the switches:


This secret also unlocks the magical bridges in the southeast corner:

This secret also unlcoks the magical bridges a bit west of the southeast corner:


You can also get the "Do it like Jones" achievement after activating a switch in the northern section and following it´s path. For further information check this

[BW] Secret 1:
After returning the pickaxe north of the camp.
Some coins, a vendor coin, a damage upgrade and ore!

Once you fell down and activated the bridge you can go west for the achievement "Daniel the Traveler". Here the location to proceed west:


Also make sure to check south and east of the level "outside" to get another upgrade and the achievement "Serious Pickup".

You also have now access to all 6 pyramids to open the pyramid to the east and get the achievement "Pyramid of Fear". For further information to these achievements and/or locations of the pyramids, please refer to this

[BW] Secret 1:
North of the broken staircase where you entered.
A shop area. Also sets your spawn point there!

[--] Secret 2:
South of the entrance. Opens after some time (once the scelettons start spawning).
A new cristal to farm!

Hey! You want the achievement "Millonaire" or "Genocide" but are tired of just repeatedly playing through the game? Well, at least thats how i feel...

So i thought, why not implement challenges. Tho they are hard to validate, i still decided to do so. And here is how it goes (created in a custom game, playing the campaign):


Challenge 1 - Feather beneath Stones

Take these challanges:

• 1 Hit point
  
• No extra lives

How the challenge works:

This challenge only measures your success through the score you reach after beating the game with these settings. In order for that, i need a screenshot of your score screen at the end.

As for now, the game has been beaten with 5 active challenges.



Challenge 2 - Bags full, no Watch or Hammer

How the challenge works:

This challenge only measures your success through the gold your character owns. The goal is, to beat the game without buying anything. In order to work, i need a screenshot where the map is open. Here is and example (in this case, the score would be 1233):


If you beat the game, make sure to take a screenshot before the score screen as you will not be able to see your current money in it, and then take a screenshot of the score screen!



Challenge 3 - Shredder

How the challenge works:

This challenge only measures your success through the combo you achieved. In order to work, i need a screenshot, where the combo is visible. Here is an example (in this case, the score would be 524):



How to submit your score:
Just add me as a friend and message me, or post on my profile that you want to submit your score, or simply put it here into the comments. The screenshots need to be public in order to work!



Every challenge will have it´s own hall of fame.
You have a great idea of a new challenge? I am listening...

Mackenzie - Score: 1,285,067





Mackenzie - Score: 54,112





Mackenzie - Score: 344,789

Well, that was it from my side.

I´d appreaciate it, if you would rate this guide. If you rate it down, please tell me in the comment section what can be changed to make this guide better.

I hope you enjoyed playing Hammerwatch as i did making this guide.
If there are any questions left, or other stuff you want to talk about, just message me or put it into the comments.

With this in mind:
Yiasmat