A naturally heated swimming pool fed by mineral springs at the centre of the Hierapolis site, with marble columns and broken architraves lying on the bottom from a building destroyed in a 7th-century earthquake. The water is 36°C year-round, lightly carbonated, faintly sulphurous, and full of bubbles that cling to the skin.
The pool sits inside a fenced complex with separate admission (paid on top of the main site ticket). Locker rooms, showers and a café are on site. Swimming among the submerged Roman fragments is a strange, slightly surreal experience and one of the few activities at Pamukkale that involves actually being in the thermal water rather than walking past it.