La Fortuna

Arenal was thought extinct until 29 July 1968, when it erupted without warning, destroyed two villages and killed eighty-seven people; it then stayed active for forty-two years, glowing at night, before falling quiet in 2010. The hot springs on its flanks are heated by the same magma, and the rainforest around it holds three per cent of the world's biodiversity in a country the size of Denmark.