The best (and most literal) example to date that red-light district Kabukichō is cleaning up its act: this sparkling-clean onsen (hot springs) complex. The tubs, which include several indoor and outdoor ones (sex-segregated), are filled with honest-to-goodness natural hot-spring water. There are several saunas, including a hot-stone sauna (ganbanyoku; ¥810 extra). Towels included. No tattoos allowed.
You can stay the night here (sleeping on a reclining armchair) for an extra ¥1840.