A nautical map – one with depth markings on it – can be a disguised dungeon setting.
It’s a dungeon, though, where the walls are in different places for everybody. If your ship draws 20 feet, you have more walls than a ship that draws 10 feet.
I really should run a ship-to-ship combat among some reefs, where instead of drawing walls, I write depths on the battlemat (or just use a real nautical map). The larger, faster ships would have to sail around some obstacles that the smaller ships could ignore.
I have everything I need to run a pretty good sea combat. I have some “Pirates of the Spanish Main” ship minis, including a few galleys; and an 8-sided wind die, marked with the cardinal directions (N, NW W, etc.)
The die came with something called “Yachting: An Exciting Game” which turned out not to be exciting and in fact is only a game in the way that Candyland is a game. In yachting, apparently, the journey from the Atlantic to a port in Cape Cod is one in which the skipper is a powerless passenger at the mercy of the cruel winds which, 7 times out of 8, run the hapless ship aground. I think this might be a misrepresentation of yachting. Cute die, though, except when I accidentally roll for damage and get “Northwest”.