The caves of São Vicente is the largest known cave system on Madeira Island. These caves were opened to the public on 1 October 1996. They were formed by a volcanic eruption; the lava came down to the sea, the outer portion was exposed to lower temperatures and solidified rapidly, while inside, the lava continued to flow with many gases and created a series of lava tubes that form the caves of São Vicente. This set of eight volcanic tunnels extends for more than 1000 metres but pedestrian course has a length of 700 meters. Inside the caves you can see volcanic stalactites, lava accumulations, known as lava cakes, and other interesting formations. The caves were discovered in 1885 and are estimated to be over 890,000 years old. There are some 30 minutes tours, unfortunately the light is really dim and taking pictures is very challenging. Probably the most interesting part is the subterrainean lakes and a curious stone named locally as “bloco errante” (the wandering stone), transported by the lava but beeing on the larger size, got trapped inside one of the pipes. Adjacent to the caves is the Sao Vicente Volcanism Centre where one can learn about the formation of the caves.