Olm

The only vertebrate in Europe that lives its whole life in caves, the olm is a pale salamander of the underground waters beneath the karst of Slovenia and the western Balkans. Its eyes are atrophied and covered with skin, yet it still senses light through the skin of its whole body and relies on other senses to find food. The slowness is the striking part: an olm can go years without eating and is thought to live for around a century. Postojna Cave keeps a few on view, and in January 2016 one laid eggs in a large aquarium inside the cave. Because olms live only in underground water, whatever drains from the surface into the karst ends up in theirs.