Saya no Yudokoro

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 ¥890 on weekdays, that qualifies as a steal. The various treatments and massages cost extra.