Go to Leap of Faith. Then, jump and go onto the outlined path. Then, go left and right and return. Once you reached the dead end, press Escape. Then, return to Leap of Faith, and walk. Lo to the left and fall. Go left or right and then forward. Go to the right path, walking backwards. Then, walk forwards and use the window. Then, go onto the dark path and follow the arrow. Then, you should get to a bright spot. Walk forwards and use the window. Then, continue walking forwards and use another window. This is how your map should look like:

Pick up the Blue Gun. Use it to do all the trials until Don't Look Down. Look down, go straight, and don't look down. Then, walk back. Get to the place where you fell when you had no gun and don't fall this time. Then walk forward and go left, then right. Go down using the platform and push the thing. Place your cube to hold the thing in place and remove your cube once you are on the platform. Don't jump, then go forward and jump through the hoop. Then, push the thing, place the cube, remove the cube, and jump. Rush through Not Enough Pieces so that you will have only one cube at the end. Place the cube and press Escape. Go to Not Enough Pieces again and return to the previous level to get a cube. Then, you should have four cubes at the end. Place them into the wall. Go forwards. This is how your map should look like:

Get the Green Gun. Remove the center and go straight. Enter the door and return. Now, get the cubes carefully and open the door in front of you. Get the cubes and open the door at the left. Go through and you should get to Strength in Numbers. Remove the edges and go through quickly. Open the door in front of you and make a square using the cubes. Repeat this until you have twelve cubes. Go to the right and go to the right. Stand very close to the door and make the cross as it used to be. destroy the two sides, then the center. Go through the door. Open the other door. This is how your map should look like:

Get the Yellow Gun. Go through the door. Do the puzzle. Go straight and open the door. Go to the special door and right-click the blue stuff. Solve the puzzle to get to Floor 2. Go to the door and click the blue stuff. Do this loop until you get to Breaking the Arc. When moving between the platforms, look at the top. Go down, then up, then down, then up. Solve the puzzle to open the door. Go through the door. This is how your map should look like:

Do the two puzzles, then go through the door. Go to the left and solve the puzzle. Then, go left and fall. Go to Stairway to Heaven. Walk straight, then right. Jump to a platform. Solve the puzzle and you are at the end. Solve the puzzles and get to the black sphere. Throw the black cube, remove it, and throw it again into the correct spot. Wait for the cutscene to end and you beat the game! After that, you could do anything you want.