Right off the bat, bathing in black water doesn't exactly sound like an attractive proposition, so we were a little hesitant when a friend recently asked us to tag along down to Ota-ku for a visit to Kamata Onsen. Found in a quiet residential area south of Kamata Station, right in between the Tokaido and Keikyu railway lines, this wonderfully old-school bathhouse looks ordinary from the outside, but is actually one of the finest soaking establishments in the area – which is renowned for its dark-as-night onsen water.
Advertised as a 'super sento' – a fancier version of your average neighbourhood bathhouse – Kamata Onsen first opened its doors way back in 1937. It's stood the test of time despite being damaged in World War II and undergoing numerous other trials, and was completely renovated exactly 30 years ago. It's speciality kuroyu baths get their distinctive colour from humic acid, an organic substance found in the groundwater under Ota and further south in Kawasaki, and are dark enough for your hand to disappear from sight only 3cm beneath the surface. These baths are also said to have the power to heal sore knees and backs, as well as improving your blood circulation and smoothening your skin.
When you're done soaking in the healing liquid, head over to the lounge for nibbles, karaoke and even gigs – Kamata Onsen hosts three to four performance nights every year, inviting local musicians and artists to strut their stuff. If you're looking to join their ranks, order some booze and start at the karaoke booth, where ¥1,000 gets you 15 songs (11 on Sundays), and watch fellow bathers join you for an impromptu sing-along session.
Kamata Onsen is open year-round and entrance is a mere ¥460 (children aged 6-12 ¥180, younger free). If you've left your towel at home, go for the ¥1,000 Tebura set, which also includes amenities and even a yukata on top of entry to the baths. Bring family or friends and get ready to explore the dark side of onsen bathing – as they say, once you go black...