Caves

The Furna do Enxofre, situated in the south-eastern part of the Caldeira da Ilha Graciosa, is an impressive lava cave, whose main feature is its perfect dome-shaped roof. The inside of the cave is reached via a tower roughly 37 metres high and containing a spiral staircase with 183 steps.

It was explored in the nineteenth century by such illustrious visitors as Prince Albert of Monaco and the naturalists Fouqué and Hartung, and is considered unique in the international panorama of volcanism and speleology. The cave's origin is associated with an important period of effusive intracrater activity of the Hawaiian type.

Inside, besides a lake of cold water, there is an important degasification field consisting of a mud pot and diffuse gaseous emanations of carbon dioxide, which are released imperceptibly in various areas of the cave floor.