A giant bath complex next to Tsutenkaku Tower in Shinsekai. The 'Europe zone' (Rome, Greece, Mediterranean) and 'Asia zone' (Bali, Persia) swap between men and women each month. There's also a swimsuit pool, stone saunas and hotel floors. Open 24 hours, so it doubles as a place to stay after the last train. Tattoos OK if covered with a sticker.
Two subway stops from Umeda and 8 minutes from Tenjimbashisuji-rokuchome Station, a natural onsen on the 8th-floor rooftop of a building. Mildly alkaline water from 659 m below fills open-air baths looking over the Osaka skyline. Generous sauna and outdoor cool-down area, ¥900 on weekdays, open until 1 am. Combine with a stroll down Japan's longest shopping arcade, Tenjimbashisuji, and Osaka Tenmangu shrine.
Eight minutes from Tsuruhashi Station, home of Osaka's Koreatown, a large bath complex known for its Japanese garden landscaping. Pot baths, a standing-depth bath, rock rotenburo and carbonated pool, plus a separately ticketed Korean-style 'hanjeungmak' stone-sauna zone. Open until 2 am — perfect after the yakiniku streets. Everything is charged to a wristband and settled on exit. ¥1,000 weekdays.
A big natural hot spring super-sentō 3 minutes on foot from Suminoekōen Station on the Osaka Metro Yotsubashi Line, right beside the Suminoe boat-race stadium. Its pride is a sprawling open-air zone fed by sodium-chloride spring water: a bamboo path, garden-style rock bath, pot tubs and a lie-down 'forest pot bath' that feel far from the city. Indoors are jet baths, an electric bath, the popular high-concentration carbonated pool, a salt sauna, hot sauna and cold plunge. Prices are modest – adults ¥800 on weekdays and ¥900 on weekends and holidays, children ¥400/¥450 – with a hand stamp for same-day re-entry. Open 10:00 to 2:00 am (last entry 1:00), all year except maintenance days. An udon-centred restaurant and rest areas are attached, and free parking for about 850 cars (3 hours with bathing, 6 with a meal). About 15 minutes by subway from Namba, it is a bayside hideaway you can drop into late after USJ or the Nankō waterfront.