Magical cave and underground lake.
When I first visited this site, there was a photo shoot taking place, complete with bikini-clad model in the turquoise pool under a palm tree, and the glamorous associations have remained with me. Even if you are not interested in geology, this 'jameo' (collapsed underground volcanic tunnel) will enchant you. Descend down some steep steps hewn out of the earth to the memorable sight of a bar and restaurant overlooking a blue underground lake. If you look closely at the water, you can see hundreds of tiny white blind albino crabs that have made their home here. Walk up the steps on the other side and you reach a funky bar that is half underground and the turquoise pool. Up some more steps is the Casa de los Volcanes (House of Volcanoes) which, rather drily it has to be said, explains some of the research that goes on into the island's volcanic activity. The gift shop is well worth a look. On most Fridays and Saturdays (check that there isn't a private party taking place), there are concerts – both jazz and classic – in the caves.