Hmm. We need some more participants... Here are some ideas to play with if you've run into a creative block (I keep thinking of other ways to tackle the challenge)...

Map a beach of sand castles.
Map a coral reef.
Map the floor and ceiling of a cave, complete with stalactites and stalagmites. (Is that even possible in isometric? Ah well, you could do them separately at least, or just the ceiling.)
Create a map (er, chart?) of a marina.
Create a map in the style of sidewalk art (the kind that seems to jump off the pavement when viewed from a specific angle).

Come on people... play! =D