How about some maps for novelty that scale to miniatures?  Perhapse a bath tub, a fountain, birdbath,  etc?

An over fillng map ie: a bird bath would play a bit like sumo. No warning of out of bounds, just drive off the side! The map could be circuler with a border passable by planes perhapse, but not by ships.

There could be added a drain for whirle pools, and you could have highly destructive colums of water as obsticals.