The natural and archaeological site in Turkey famous for white travertine terraces is Pamukkale.
Pamukkale, meaning “cotton castle” in Turkish, is a dazzling formation in Denizli Province created by mineral-rich thermal waters. As the hot water flows down the hillside, dissolved calcium carbonate precipitates and gradually forms travertine terraces, pools, petrified waterfalls and bright white deposits. The landscape is natural, but the World Heritage property also preserves a major ancient city.
The ruins of Hierapolis sit above the terraces. Founded as a thermal spa by the Attalid rulers of Pergamon in the late 2nd century BC, Hierapolis later flourished under Greek, Roman and Byzantine rule. Its remains include baths, temples, a theatre, a large necropolis and the Martyrium of Saint Philip.
Strictly speaking, UNESCO’s official name is “Hierapolis-Pamukkale,” a mixed natural and cultural site inscribed in 1988. Pamukkale is nevertheless the fair canonical answer because the question identifies the site through its most recognizable feature—the white terraces. Göreme, Ephesus and Cappadocia are separate Turkish heritage destinations.