Caldeira da Graciosa (Furna do Enxofre). 16/06/08; Archipiélago de las Azores; 120 ha; 39°01'N 027°58'W. UNESCO Biosphere Reserve. A volcanic crater on Graciosa island, one of the largest of its kind with a perfect vault, containing on its bottom a lake of cold and sulphurous freshwater. It constitutes a rare example of cave and lake with volcanic activity of small geysers inside. There are important native and endemic species of arthropods characteristic of this habitat and the endemic species of bat Nyctalus azorica can also be found there. The cavern Furna do Enxofre (on the World Heritage tentative sites list) is the high point of the island for tourists, and the access to its grounds is made in circles through the stairs of a curious tower built in the cave. Ramsar site no. 1798. Most recent RIS information: 2008.