Västerås, Sweden: The ultimate lake house
If you're willing to swap space for location, the views at Mikael Genberg's art project-slash-hotel the Utter Inn—both above deck and below—are pretty unbeatable.
Not for claustrophobics, the one-room inn is about a half-mile out from Sweden's port town of Västerås, on (and in) Lake Mälaren. Once you've been ferried over by boat, make yourself at home: Sunset cocktails on the wraparound deck are nice. You can motor into town via dinghy for dinner, or have a meal dropped off.
Come bedtime, it's a short climb down a ladder to the underwater chamber 10 feet below: Here, from the comfort of twin beds, you can watch the fish as they're watching you.
The season's wrapping up at the Utter (the hotel closes from November through March), but crisp autumn is one of the loveliest times to visit. (And don't worry, the inn is outfitted with a camper stove and underfloor heating.)