At 37 miles west of Austin (Texas, USA) is located one of the most unusual and picturesque lakes in the world - Hamilton Pool (Hamilton Pool). The singularity of it is that it is both an underground lake and land, come to the surface from under the stone arch grotto. Complements the beauty of a waterfall flowing from the 15-meter-high lake was formed thousands of years ago as a result of the collapse of the limestone dome of an underground river due to massive erosion. Water underground rivers flow into the river flowing nearby Pedernales (Pedernales river), which in turn is a tributary of the Colorado River