Saya no Yudokoro
Time Out says
Fed from a natural hot spring 1,500m under ground, the water at Itabashi's top onsen facility is rich in sodium chloride, giving it a characteristic greenish-brown colour. But this health-bringing elixir isn't the only thing worth noting at Saya no Yudokoro: its renovated, traditional-style buildings and zen garden are gorgeous, as is the rotenburo (open-air bath), which is surrounded by lush greenery. The facilities include both dry and steam saunas, a hot stone spa and a restaurant with views over the garden. For ¥870 on weekdays, that qualifies as a steal. The various treatments and massages cost extra.
3-41-1 Maenocho, Itabashi-ku
|Transport:||Shimura-Sakaue Station (Mita line), exit A2|
|Price:||Mon-Fri ¥870, children ¥550; Sat, Sun & hols ¥1,100/¥750|
|Opening hours:||10am-1am daily|