Pamukkale is in inland southeastern Aegean Turkey. Pamukkale, which has been used as a spa since the second century BC, literally means “cotton castle” in Turkish. The travertine features have their origins in the shifting of a fault in the valley of the Menderes river (between here and Denizli). As the fault shifted, very hot springs with a very high mineral content (notably chalk) arose at this location. Apart from the slightly radioactive minerals, the calcium and hydrogen carbonate react to create calcium carbonate (also known as travertine) and limestone. This is what gives Pamukkale its whiteness and created the pools.