In deepest Tuscany, a sulphurous river spills over a staircase of milky-blue travertine pools beside an old mill, holding a steady 37.5°C in any weather — and it's free, open around the clock and gloriously unmanaged. Claim a tier, wedge yourself under a mini-waterfall and let the current do the massage. Winter mornings are the smart slot: steam rising, frost on the fields, hardly anyone about. Leave the silver jewellery at home; the sulphur tarnishes it black.
Featured in Ten wild swimming and water adventures across Europe · Adventure