While the sight of these gorgeous pools may make you want to don a swimsuit and plunge in for a refreshing soak, we don"t recommend it. The water may be fed by underground geothermal springs, but these are no hot springs—the water"s only about 41 F. We"ll take it all in from dry land. The terraced, travertine pools cascade downward for nearly 2 miles. Formed over thousands of years, calcite deposits give the water its unique, and welcoming, turquoise coloration.