At first, I didn't want to reveal this one, but now that it has been a while ago since the level came out, here's the entire solution.
The challenge is build out of 5 smaller challenges.
1. Finding the cave
The first challenge would be to find the cave itself. I actually marked the screen the cave is on by adding a diamond made out of 4 colours, as sort of background image. In the game, there's this big room where you must jump down, get over a laser and lateron when having the eye, you must get up again. On the top left before you jump down, you'll notice the diamond on the right. In the corridor towards this big room, there's a secondairy room that you'll have to jump into. Once you found it, a note will tell you that you made it.
2. Timing part 1.
The cave consists out of 4 challenges, of which 2 are timing skills. At first, it may seem hard, but stay calm and time when you have to jump. I can easilly jump from block to block while the lasers do their thing, but if you really have some difficulty, then you can use the following trick: jump when the laser is out, move to the right edge of that block and wait for the laser to come on. You can stand on that block with the laser on if you're far enough to the edge. At the end jump, you can jump against the wall and stick there if you find that necessary. The same technique can be used to cross back.
3. Timing part 2
The level starts with a series of jumps. While the laser is out, you can stand on that part. Timing is essential like in the previous part, but in this stage, you cannot cheat. Luckelly, the area isn't as big as the previous one. Practice and stay calm. When coming up, first jump over the laser and wait at the second laser. You'll have to time your movement to the moving laser and the other laser so you can get past. Notice that there's a small gap on the place where it doesn't spray. That'll be your safety zone. Time your jump and you should be able to get all the way up there without much problem.
4. The black screen
From the top, jump to the right until you are walking on the cloud. Jump to the higher part. Try and feel where it ends and exactly at the end jump up right. The passage is a bit tricky but you'll find it, once you know where to look for.
5. The yellow maze
As you might read further in this topic, there's a map located for the yellow maze. Basically some parts of the grid will kill you while others will not. It might seem to be a tedious task figuring out which will and which won't kill you. Thats where the map comes into play.
The map can be found after jumping down in the big room (past the horizontal red lazer) then through the 2 lasers door. the next room has this big coloured image on the top. You might recognise it now. Yes, this is your map. It shows you a path that has a dead end. This should tell you that there's no point in going through that route. Finding the path on your own will also tell you that its the wrong way. You can get back though, cus some of the yellow borders are only deadly on the side so you can still partially jump on them.
How to solve this? Its very tricky actually. Before you are about to warp to the yellow room from the previous challenge, don't. Instead, walk through the secret room on the right. This will bring you to the left side of the yellow maze. Use the map to jump to the transporter on the left and use it.
The next room doesn't has a challenge. Walk to the statue and let it tell you the cheatcode. You can die though if you jump ahead of the teleporter. There's nothing there other than your way back into the level.