I keep the idea of the cave art and now skyscraper will be a second key element. The contrast is quite interesting and as I lived in a city with a lot of tall buildings, research doesn’t need much time anymore.
The question which has to be answered is:
Why is the cave art undiscovered?
To answer with concept art you need some additional constraints to “stay in the track”:
No cave art on the floor, because movement will be weird when you have multiple axis with gravity and no gravity is also weird (the movement is actually not defined yet but I have the idea of a platformer in my head)