It is a natural site in Denizli Province in south-western Turkey. The city contains hot springs and travertines, terraces of carbonate minerals left by the flowing water. The ancient Greco-Roman and Byzantine city of Hierapolis was built on top of the white "castle".
The unique formations of travertine (calcium carbonate) shelves, pools and stalactites, which hug the ridge above town like a white scar, were created by the area’s warm mineral water, which cools as it cascades over the cliff edge and deposits its calcium. It’s a strange piece of landscape unlike anything else you’ll see in Turkey, and it now appears on the Unesco World Heritage list.