I love the game Spelunky! It's a 2D platform famous for its difficulty. The art, the music, the controls, the gameplay is just splendid and I often wondered in what direction the game would take if it would transcend into 3D space. The only thing that popped into my mind was Mario Galaxy. I think the style would do Spelunky well, but gameplay wise I am still not sure if it would work in 3D. But Mario did the jump from 2D to 3D, so why not Spelunky.

However, I don't think this spherical map style would work for a normal Spelunky level, but it could be a sort of a hub world, like in Mario Galaxy. A Hub world that connects to other levels that has a more normal camera & conventional level design used in Mario 64 etc. Great, fun image to work on!

 

I made this quick 3D block mesh as a reference and then painted on top of that.

I made this quick 3D block mesh as a reference and then painted on top of that.