Hotels as destinations?

Sure, for many people a hotel is just meant to be a base where they unpack and rest after a full day out exploring their surroundings. However, some types of lodging can be just as much a part of the adventure as an afternoon at the museum or a walking tour. At least that's the case when the place you call “home” for the time being happens to be a room in a Victorian or gothic castle, a cell in a prison, a quarter in a monastery or even on a giant pirate ship. When your lodgings are THAT interesting, you don’t need to feel particularly guilty about hitting the hay early and resting your tired feet. Or sleeping in.

What is the most interesting or unusual place you've stayed in?