Spas with reservation required in Japan

Shibu Onsen, Nagano

Reservation-only private hot spring and sauna suites at a Nagano brewery complex, built around a craft beer bathing plan for two to four guests.

Tokyo

Private-room head spa salon in Minami-Aoyama, Omotesando, offering 90- to 210-minute scalp treatments from roughly ¥24,750.

Arima Onsen, Hyogo

Hotel spa in Arima Onsen with Arima's rare iron-rich "ginsen" waters, outdoor baths, sauna and jacuzzi, run as an all-inclusive overnight stay.