Learn the Japanese phrase "Atsui desu" ("It's hot")

Bathing in Japan is more than the national pastime; it's a national obsession. Visiting onsen, or natural hot springs, is the ideal immersion. Part of a 1,500-year purification tradition with roots in Buddhism and Shinto, onsen also provide the perfect casual atmosphere for socializing with the Japanese. Remember one simple rule and you'll be welcomed like a local: Wash at the shower stations outside the daitsuba (changing rooms) before you bathe. Sitting on a small stool, soap and scrub yourself from head to toe (soap is usually provided, but it's a good idea to pack your own, along with a washcloth). As a foreigner, you might want to make a long show of washing, since the Japanese often assume that we gaijin don't know enough to cleanse ourselves prior to bathing. Before getting in the water, wring out your washcloth and use it to preserve your modesty, like Eve with a fig leaf. Rotenburo, or outdoor baths, are especially prized for their open-air settings; often they face a mountain or overlook the ocean. Be careful: In Japan, the "very hot" classification is 108 degrees or above—hotter than what most Westerners find comfortable. The Japanese consider that bathing nirvana is achieved at the yudedako, or "boiled octopus," stage. Place a folded washcloth on your forehead to keep cool.