Pamukkale Thermal Baths, also known as the Cotton Castle, is a naturally occurring thermal spring in Denizli, Turkey. The thermal baths are located on top of a mountain ridge, and are known for their stunning white travertine terraces and blue-green thermal pools. The waters of Pamukkale are said to contain healing minerals that have been used for centuries to treat a variety of ailments. Visitors can soak in the thermal pools, or explore the ancient city of Hierapolis, which is located nearby.