Kitashinagawa Spa Tenjinyu

北品川温泉 天神湯 A small sento with kuroyu onsen water, not far from Shimbamba and Aomono-yokocho stations. Here's the water analysis and onsen certificate: http://www.tenjinyu.com/spa.html "The black hot spring water, pumped from 100 meters underground, is natural hot spring water consisting of organic matter decomposed from plants dating back to the Paleozoic era, slowly dissolved into groundwater over time. It is characterized by containing minerals bound to organic substances that do not break down even when brought to the surface. The rich minerals gently act on the skin, keeping it moisturized and smooth even after bathing." Went because we had errands nearby and I saw in the Google Maps FAQ that tattoos are allowed. Indeed, empirically confirmed — tattoos are OK. Loved the kuroyu, will go again. Facts: Visits recommended to be limited to 1 hour. Inside: two baths with jets and a separate room with kuroyu. Price: 550 yen. Towel rental available. Lockers: 100 yen with refund. Hair dryer: 10 yen per 2 minutes. Hours: 15:00 to 23:00. Bicycle parking available.