These underground tunnels are more than 1km (0.6mi) in length and were formed when the outside skin of a molten-lava flow solidified. When the flow ceased, the molten lava kept moving inside, emptying out of the skin and leaving tunnels. They're on private property and can be visited without an official guide - the owners of the land provide information, guides and flashlights. Tours are also offered in Puerto Ayora.
