On the Spree River at Treptower Park, Badedampfer runs six self-drive hot tub boats and the Saunadampfer, a floating sauna that small groups rent privately. General manager Roxy tells how founder Jannis, then 24, sketched the first boat with an artist friend and spent months cycling across Berlin looking for a place to moor it. The hot tub boat came first, and the sauna followed. Between rounds of heat, guests jump straight into the river with the TV Tower in view and the city surprisingly quiet around them. With the Berlin station now at full capacity, Badedampfer is preparing to open new stations in other German cities and abroad.