In the lake, which has a diameter of 130 metres, the level of water and sulphurous gases varies during the year. It is best to visit the cavern between 11 am and 2 pm when the sun penetrates the interior, providing ideal conditions for observing the splendour of this cave, unique in the world.

In 1879, Prince Albert I of Monaco, a student of oceanography, was one of the first to go down into the Furna do Enxofre.

It is possible to visit other volcanic phenomena on Graciosa, including the Furna do Castelo, also known as the cave of Maria Encantada, situated on the highest point of the Caldeira or crater and consisting of a lava tube around 60 metres long (which is said to have been inhabited when the island was first settled) and the Furna da Lava or the Abel cave, located in Canada das Furnas and consisting of a lava tube almost 100 metres in length in which light enters through two places where the ceiling has fallen in.

For those who enjoy being in close contact with nature and the scent of mystery that permeates the Azores, the opportunity to explore Graciosa and its cavern is a powerful attraction.