In the Cave 

Lanzarote, The Cave of Los Verdes or Spanish The Cueva de los Verdes or Green Caves are part of the Atlantida underground Cave system formed some 3000 years ago during the eruptions of the Corona Volcano (in the north of Lanzarote). The original inhabitants, often referred to as the Guanches, and later the Hispanic population, would shelter here from Pirates that once tormented the Island.

The tunnel is over 6 km long with an additional 1.6 km under the sea and is one of the longest Volcanic Tunnels in the World (the underwater section has not been fully explored), although only about 2 km are open to the public.
The cave measures more than 15 meters wide and 15 m high.

The Caves are not named after the colour Green, but rather a family whose surname was Verde (Green), although the Caves are indeed colourful, especially since they have been carefully and thoughtfully artificially lit for the public.