Low on ideas, but got something working
Ah, I had a reasonable sleep, now to work again
I tried to come up with some very cave-like gameplay, but it all seemed rather dreary. It seems to me that caverns is goign to be mroe of a setting than a gameplay mechanic.
Anyways, 2D platformer. I have 2 superimposed such that the player is interacting with only the frontmost at any given time. Pressing spacebar will instantly reverse the order of the two caves, creating hopefully interesting gameplay.

Making it pretty is tomorrow’s work. Storyline is unneeded.
Oh, and check out the awesome realtime value sliders and the restart button that reloads all scripts and restarts the game, pretty convenient if you ask me.