Sistema Sac Actun (Mexico) – Located in the Yucatán Peninsula, it's one of the world’s longest underground rivers, connected to ancient Mayan cenotes. Lost River (USA – Indiana) – This river vanishes ...

This serial property is an unusually well-preserved and extensive epigenic gypsum karst terrain. It includes a very high density of caves: over 900 caves in a relatively small area, with over 100 km ...