Shimizuyu (Musashi Koyama Onsen)

Get the full onsen experience at sento prices in this neighbourhood bathhouse in south-west Tokyo. Shimizuyu used to offer only the inky black kuroyu water that's typical in this part of the city, but they tapped into a deeper spring during an extensive overhaul in 2007, meaning that you can now also bathe in iron-rich 'gold' water in the outdoor rotenburo. At ¥460 (¥180 for children), it's a steal, though the price shoots up if you want to use the saunas (one of which, a Korean-style hot stone variety, is for ladies only).