Red key: Go to the room with the gate. At the base of the middle pillar on the left, find a little red switch. Left click and drag to any position. This will raise a platform. The key is under the platform.

(Bonus objective: Coin. Jump on the platform and grab the coin near the ceiling.)

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Blue key: Go back to the previous room. As you're facing the room with the red key, look at the right corner of the room you're in now. Notice how the wall juts out? Look at it closely while you hit "left shift", and you'll see the V switch.
Go into door V and hit the nearby switch on your left, which opens a door, muscle past the spheres, and head up the ramp.

(Bonus objective: Coin. Use the big rock to get up onto the platform and grab the coin.)

Go through the new door on your right. You enter a room with platforms, and can see the blue key on the other side of a set of doors at the far end! If you fall to the blue floor (water?), it resets you to the start of the room. There is no penalty for falling other than that.
Sprint (ctrl + W) to get momentum to reach the first platform, then jump normally to the next ones. You might have to sprint to get to that fourth platform (the one which opens into a tunnel.) Up the ramp and over the bridge, then sprint-jump from the bridge to the alcove. Hit both buttons to open the door and grab the key!

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Green key: The first pillar on the right in the third room (the one with the red key) has a switch about halfway up. Hit that, then go to the previous room and through the door with the X on it.
On the wall to the left of the door is another switch. Hit that to power up the platform at the back of the room. Jump on the platform (which will automatically raise up) and hit a third switch on the left side, in the colorful thing. As with the blue room, sprint-jump from the raised platform to the now-open doorway.
Hit the button on the wall to your left, which will raise the gate on the other side. Ride the moving platform across, and lay hands on the green key!
Jump down to the weird slippery green floor, run out through the tunnel and into a very familiar area.

(Bonus ojective: Coin. Just as you enter the tunnel, look behind the big rock in the corner.)

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Back in the key room, smack the buttons with the key symbols, slam the big red button to the left of the gate, and... I'm not going to spoil that for you.



Thanks for reading! Please upvote if this helped you.