The ancient city of Hierapolis was built on top of the white "castle" which is in total about 2,700 metres (8,900 ft) long and 160 metres (520 ft) high. It can be seen from the hills on the opposite side of the valley in the town of Denizli, 20 km away.
Tourism is and has been a major industry. People have bathed in its pools for thousands of years. As recently as the mid 20th century, hotels were built over the ruins of Heropolis, causing considerable damage. An approach road was built from the valley over the terraces, and motor bikes were allowed to go up and down the slopes. When the area was declared a world heritage site, the hotels were demolished and the road removed and replaced with artificial pools. Wearing shoes in the water is prohibited to protect the deposits.
Pamukkale's terraces are made of travertine, a sedimentary rock deposited by water from the hot springs.
In this area, there are 17 hot water springs in which the temperature ranges from 35 °C (95 °F) to 100 °C (212 °F). The water that emerges from the spring is transported 320 metres (1,000 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 240 metres (790 ft) to 300 metres (980 ft). When the water, supersaturated with calcium carbonate, reaches the surface, carbon dioxide degases from it, and calcium carbonate is deposited. The depositing continues until the carbon dioxide in the water balances the carbon dioxide in the air. Calcium carbonate is deposited by the water as a soft jelly, but this eventually hardens into travertine.
This reaction is affected by the weather conditions, ambient temperature, and the flow duration. Precipitation continues until the carbon dioxide in the thermal water reaches equilibrium with the carbon dioxide in the atmosphere. Measurements made at the source of the springs find atmospheric levels of 725 mg/l carbon dioxide, by the time this water flows across the travertines, this figure falls to 145 mg/l. Likewise calcium carbonate falls from 1200 mg/l to 400 mg/l and calcium 576.8 mg/l to 376.6 mg/l. From these results it is calculated that 499.9 mg of CaCO3 is deposited on the travertine for every liter of water. This means that for a flow rate of 1 ı/s of water 43191 grams are deposited daily. The average density of a travertine is 1.48 g/cm3 implying a deposit of 29.2 dm3. Given that the average flow of the water is 465.2 l/s this implies that it can whiten 13584 m2 a day, but in practice this areal coverage is difficult to attain. These theoretical calculations indicate that up to. 4.9 km2 it can be covered with a white deposit of 1 mm thickness.
The terraces became damaged after years of tourists climbing on them
The former Roman Bath of the ancient city of Hierapolis has been used as the site of the Hierapolis Archaeology Museum since 1984.
In this museum, alongside historical artifacts from Hierapolis, there are also artifacts from Laodiceia, Colossae, Tripolis, Attuda and other towns of the Lycos (Çürüksu) valley. In addition to these, the museum has a large section devoted to artifacts found at Beycesultan Hüyük that includes some of the most beautiful examples of Bronze Age craft.
Artifacts from the Caria, Pisidia and Lydia regions are also on display in this museum. The museum’s exhibition space consists of three closed areas of the Hierapolis Bath and the open areas in the eastern side which are known to have been used as the library and gymnasium. The artifacts in open exhibition space are mostly marble and stone.
Pamukkale is a tourist attraction. It is recognized as a World Heritage Sites together with Hierapolis. A few other places in the world resemble it, including the Mammoth Hot Springs in the USA and Huanglong in Sichuan Province of China (another UNESCO World Heritage Site). Hierapolis-Pamukkale was made a World Heritage Site in 1988.
The underground volcanic activity which causes the hot springs also forced carbon dioxide into a cave, which was called the Plutonium meaning place of the god, Pluto. This cave was used for religious purposes by priests of Cybele, who found ways to appear immune to the suffocating gas.
Tadpoles can be found in the pools.