Tsingy de Bemaraha national park in Madagascar has a forest of limestone pillars. The word tsingy means “where one cannot walk barefoot.” Water eroded caves and passages through the land, the roofs of which eventually collapsed and left the pillars standing up to 70 meters tall. The tops of the rocks have a vastly different ecosystem from the valleys, and from the surrounding savannahs. The stone forest is home to thousands of species not seen outside of Madagascar. Image by Stephen Alvarez for National Geographic.