Just a thought (don't know if this has been suggested previously) - how about a challenge map where you have to defend the tavern itself? There are two doors in the ground floor after all, so those could be spawn points. The tavern keeper himself could also need defending (similar to the boss fight in Etherian Holiday Extravaganza).

If the area is too small, perhaps the outside of the tavern could be fully modelled, with the doors as the entry points into the tavern itself?

What do people think?