Pamukkale

Pamukkale, meaning "cotton castle" in Turkish, is a formation of brilliant white travertine terraces in Denizli Province, southwestern Turkey, built up over hundreds of thousands of years as calcium-carbonate-rich thermal spring water flowed down a hillside and precipitated calcite as it cooled and degassed carbon dioxide on contact with the air. Each cascading terrace and shallow pool traps a thin sheet of mineral-laden water whose slow evaporation and continued precipitation build up crystalline calcium carbonate in successive layers, gradually forming the stepped, basin-like structures and stalactite-like formations that cover the hillside. The same geothermal system that feeds the terraces also underlies the adjacent ruins of the ancient spa city of Hierapolis, and the site was jointly inscribed as a UNESCO World Heritage Site for both its natural travertine formations and its archaeological remains.