It may look like an arctic tundra, but this mineral-rich hot spring in Turkey is anything but frigid. Pamukkale's blue pools, which cascade over pearly cliffs, attract millions of visitors each year.

Pamukkale means "cotton castle" in Turkish, and it's been a spa and spiritual center since Roman times. Modern-day visitors still seek out the mineral-rich springs for their medicinal qualities, and believe that they can ease the symptoms of illnesses from arthritis to high blood pressure.

Though it looks like sheets of ice, the pools are actually created by underground volcanic activity. When water flows over the sides of the terraces, it cools to form ridges of hard, white calcium. The water temperature remains consistent at about 95 degrees Fahrenheit (35 degrees Celsius), so guests can comfortably splash around even in winter.=

When to go: The best time to visit Pamukkale is in the fall, when the busloads of summer tourists have headed home. If  you do decide to come in the summer, plan your visit for the early morning before the sun gets too hot. Visitors can take a 20 minute bus ride to Pamukkale from the town of Denizli, with buses running every 15 minutes. If you are coming from Istanbul, a flight to Denizli might be preferable to the 10 hour bus ride.

What to know: The Pamukkale pools are open from 8am–8pm daily (until 5pm in the winter). The entrance fee is $6 and changing rooms are provided. Be sure to bring a bathing suit and towel – and sunscreen.