Coral Castle is a stone structure in Homestead, Florida created by the Latvian immigrant Edward Leedskalnin. Compared to Stonehenge, ancient Greek temples, and the great pyramids of Egypt, Coral Castle was built of coral blocks weighing as much as 30 tons. Working alone and only in the night refusing to allow anyone to view him while he worked, Leedskalnin, 5 feet (1.52 meters) tall and weighed about 100 lbs (45 kg), labored for 30 years from 1920 until his death in 1951.

Coral Castle on Wikipedia
Coral Castle Museum