In the tropical adventure Ransom of the Seven Ships, Nancy free climbs a mountain perforated with bat-filled caves while being bombarded with coconuts flung by monkeys at the summit. Intense, I know. The mountain is only ever seen as a 2-D background upon which our heroine clambers, but the caves and obstacles Nancy encounters needed to be worked out on paper beforehand.
Next, I had to imagine that 3-D mountain environment was spread out on flat surface, and work using a mix of textures and painting in order to carve out the nooks and crannies Nancy would have to traverse to get to the top.
Here's how the players see it in game.