SPAWORLD, JAPAN

Naked truth: Volcanically active Japan has thousands of natural hot springs traditionally enjoyed au naturel. One Osaka onsen has taken that concept to the extreme, creating an over-the-top, around-the-naked-world-in-eight-floors theme park. The complex is divided into themes by country—Finland, Greece, Spain, France, Ancient Rome, and so on. You'll soak amid a replica of the Trevi Fountain, in a hammam-meets-Disney stone bath, and over an Atlantis-themed tank full of tropical fish. Naturally, all baths and body soaks are done in the nude, but—bummer alert—men and women are confined to separate floors. On the bright side, you're given pj's to wear when you walk around the common areas—pink for girls, blue for boys.

Bodies of evidence: Despite its name, SpaWorld is favored by locals—and it's popular. Expect to be hanging with lots and lots of naked Japanese people.

Best reason to bring a towel: The ones they supply are meant for locals. Hearty Americans may find the in-house towels only cover one cheek.

Don't forget your: Japanese-English dictionary. This will be especially useful for translating the following: "Pardon me. I'm straight, but may I join your all-male naked pool party?"

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