Where In The World Is ... Cotton Castle?

For over 2,000 years, people have journeyed to a fantastic hillside that appears to be draped in a frozen waterfall. But it isn't cold, and what you see isn't ice: Rather, it's one of geology's most head-scratching optical illusions. Cascading down a hillside are dozens of bright white terraced pools, each one filled with warm, turquoise water.

Thousands of years ago, a mighty invading culture built an entire city on top of this natural wonder, transforming it into one of their most popular healing destinations. They believed the warm, mineral-rich waters could cure everything from skin conditions to heart disease. Wealthy citizens would travel hundreds of miles to bathe in these ethereal pools, and the tradition continues today, although contemporary visitors come as much for the otherworldly beauty as for any supposed therapeutic benefits.

The science behind this "cotton castle" is surprisingly simple, yet it took thousands of years to create. Hot springs carrying dissolved limestone emerge from the hillside at temperatures around 95°F. As the water flows down the slope, it gradually cools and deposits calcium carbonate, slowly building up the brilliant white travertine terraces. Each pool edge grows by about 1 millimeter per year, creating the stepped formation that gives this place its fairy-tale appearance.

This is Pamukkale in southwestern Turkey, whose name literally translates to "Cotton Castle" in Turkish, a fitting description for formations so white and fluffy-looking that early travelers thought they were seeing snow. The site combines natural wonder with human history: The ancient city of Hierapolis sits directly above the thermal pools, creating a UNESCO World Heritage Site that spans both geological and archaeological treasures.

Ready to soak in history's most beautiful bathtub? Tell us in the comments!

Senior writer Chris DeWeese edits Morning Brief, The Weather Channel’s newsletter.