Among the state’s most notable caves is the extensive limestone system under the Nullarbor Plain. Centred mainly on Ceduna, it is closed to the general public but can be explored by experienced cavers who have obtained a permit from the national park authorities. In the south of the state, the flooded caves of Mount Gambier are a venue for cave diving, a particularly dangerous form of caving. Nearby is the town of Naracoorte and the Naracoorte Caves Conservation Park, where tunnels and chambers are open to tourists as well as adventure cavers.