Pamukkale's white travertines were formed by mineral-rich thermal water which flow down the hillside. As the water cools, the mineral sediment forms white travertine pools, from which this place takes its name, "Pamukkale," meaning "Cotton Castle." The ancient city of Hierapolis stands on the terrain above these pools. Hierapolis was a major city in ancient times, and is also the site of one of the seven churches addressed in the Book of Revelation. A third site, in the nearby town of Karahayit, also has travertines and mineral pools and can be accessed from Pamukkale by dolmus (a shared taxi).