As in a Jules Verne adventure, exploring the centre of the Earth requires a combination of risk, hard work and curiosity. These mysterious caverns will reveal all their secrets only to cavers. This climbing discipline entails the study and inspection of potholes and caves. Cavers must determine the length and depth, amongst other important parameters, and have technical knowledge, the right equipment and a knowledge of the area being explored, and of the weather conditions. Some caves can be entered on foot and do not require any complex equipment: just the appropriate clothing, a helmet and light sources. There are many different types of cavity with varying difficulties, although there are three main types. The first is the gallery, a horizontal passage that may be steeply sloping and of a variable size: from centimetres to passages measuring hundreds of metres in width and fifty metres in height. There is also the shaft, a vertical passageway, and the chamber, which tends to be large. To practice this sport you are advised to contact the Federació Catalana d’Espeleologia (Catalan Caving Association), which offers courses. They also have information on the types of caves that can be visited, including caves of interest due to the presence of wild fauna such as bats, as in the case of the Vallmajor cave in Albinyana in the Baix Penedès region, and the Daví and Castellsapera chasms in Sant Llorenç de Munt. They can also tell you which ones have low oxygen and caves with a special visiting schedule, like the shaft of La Calella, located in the heart of L’Estartit in Girona.