Sakaeyu

While other onsen in Tokyo are inclined to be conservative with their precious hot spring water, that isn't the case at this dowdy public bath in Sasazuka, just one stop down the line from Shinjuku. At Sakaeyu, even the taps and showers dispense pure onsen water – a generous profligacy that goes some way to compensating for the cramped dinginess of the place. The facilities include a medicinal bath – which might be imbued with lavender, wine, green tea or herbs, depending on which day you visit – and a sauna, the ¥300 premium for which includes free towel rental.