The brainchild of local artist Mikael Genberg, the Hotel Woodpecker is a tiny treehouse in a public park in the town of Västerås, Sweden, about 62 miles from Stockholm. Over 40 feet up in the air, the little cabin (complete with wee kitchen and toilet) is designed for one guest, but it can hold two if you don't mind serious intimacy. Staying at the Hotel Woodpecker also involves serious commitment, as once you get up, as you must get hoisted up using the block-and-tackle technique, and remain stranded until a set appointment time to descend. Meals arrive via a rope basket. 011-46/70 775 53 93, mikaelgenberg.com, deluxe about $135, includes breakfast and dinner, closed in winter. Also, the Tourist Office of Västerås can book reservations (011-46/21 39 01 00).
Black Tulip Hotel
The Black Tulip is billed as "Europe's Most Luxurious Gay Leather & Art Hotel," but it's not the luxury, the art, the gay, nor even the leather that makes Amsterdam's Black Tulip scary. It's the pain. "Leather" rooms are kitted out in more than just cowhide, sporting all kinds of equipment for the cheerful bondage enthusiast. You'll never look at a "puppy cage" the same way again. On the plus side, there's a minibar/fridge in every room, perfect for storing cold compresses. 011-31(0)20 4270933, blacktulip.nl, from $160, includes breakfast buffet.
At Karosta Prison, the Latvian city of Liepaja , the rooms are indeed jail cells, largely unchanged since the last real prisoners left in 1997. The KGB ran the place in the 1970s, and the tradition of hospitality lives on: Should you choose the "extreme overnight" stay, you will undergo questioning, an inspection by the prison doctor, confiscation of your belongings, and a sleepless night on a pillowless, blanketless bunk. The occasional warning shot fired in the air may further disturb your slumber. Did we mention the delightful prison toilets? 011-(371) 6369470, karostascietums.lv, $10.
Propeller Island City Lodge
Berlin's Propeller Island City Lodge takes the art-hotel concept to the lunatic fringe. Some rooms are merely whimsical, like the pink "Chicken Curry" room or the one featuring a bed shaped like a castle. Others are only mildly irritating, featuring inclined floors, monochromatic colors, or hanging beds. Still others are downright fiendish, such as a blindingly bright room covered with faceted mirrors or a simple pair of coffins meant to invite "rest." Rates vary widely depending on room size and your tolerance for the zany. 011-49/(0)30 891 90 16, 011-49/(0)163 256 59 09, propeller-island.com, from $95.