The best evidence that Kabukicho is cleaning up its act: a gleaming onsen complex right in the heart of Tokyo's former red-light district. The tubs — both indoor and outdoor, sex-segregated — are filled with genuine natural hot-spring water. Several saunas await, including a hot-stone ganbanyoku. Towels are included in admission. It's the ultimate contrast: soak in volcanic waters, then step outside into the neon blaze of Shinjuku's most electric neighbourhood.