Pamukkale, Turkish for "cotton castle", is a slope of blinding-white terraces where warm, calcium-rich spring water has been turning itself to stone for thousands of years. Seventeen springs rise here between 35 and 100°C, so saturated with dissolved limestone that they leave a fresh crust of white travertine wherever they flow. Each terrace cups a shallow pool of turquoise water, and the whole formation steps down almost 200 metres to the Denizli plain — from a distance a frozen waterfall, or the cotton castle of its name. Crowning the ridge is Hierapolis, the Greco-Roman spa city that the Attalid kings of Pergamon founded around these healing waters late in the 2nd century BC, leaving a monumental theatre, a colonnaded street, and one of Anatolia's largest ancient necropolises. Pamukkale and Hierapolis were inscribed together as a single UNESCO World Heritage Site in 1988.
You walk the travertines barefoot — shoes are banned because they grind and stain the growing surface — and warm water runs over your ankles while the white stone gleams in the sun. To protect the fragile terraces, only a marked path stays open and many of the pools are kept dry or filled in rotation, so a slope of brimming basins is not what every visitor finds. At the heart of Hierapolis, the Antique Pool lets you swim in warm mineral water among marble columns and Corinthian capitals that slid in when a 7th-century earthquake toppled the Temple of Apollo. Come late in the day: the crowds thin, and the low sun washes the whole slope pink and gold while the pools mirror the sky.