Pamukkale, meaning "cotton castle" in Turkish, is a natural site in Denizli Province in southwestern Turkey. The area is famous for a carbonate mineral left by the flowing of thermal spring water.It is located in Turkey's Inner Aegean region, in the River Menderes valley, which has a temperate climate for most of the year. he ancient Greek city of Hierapolis was built on top of the travertine formation which is in total about 2,700 metres (8,860 ft) long, 600 m (1,970 ft) wide and 160 m (525 ft) high.
It can be seen from the hills on the opposite side of the valley in the town of Denizli, 20 km away. Known as Pamukkale (Cotton Castle) or ancient Hierapolis (Holy City), this area has been drawing visitors to its thermal springs since the time of Classical antiquity. The Turkish name refers to the surface of the shimmering, snow-white limestone, shaped over millennia by calcite-rich springs.
Pamukkale's terraces are made of travertine, a sedimentary rock deposited by mineral water from the hot springs. In this area, there are 17 hot springs with temperatures ranging from 35 °C (95 °F) to 100 °C (212 °F). The water that emerges from the spring is transported 320 metres (1,050 ft) to the head of the travertine terraces and deposits calcium carbonate on a section 60 to 70 metres (200 to 230 ft) long covering an expanse of 24 metres (79 ft) to 30 metres (98 ft). When the water, supersaturated with calcium carbonate, reaches the surface, carbon dioxide de-gasses from it, and calcium carbonate is deposited. Calcium carbonate is deposited by the water as a soft gel which eventually crystallizes into travertine.