It's one of the most dangerous sports in the world but that knowledge does nothing to deter thrill seekers diving to discover the hidden underwater passages that lie far beneath us.

Highly trained and highly equipped, cave divers come to Tank Cave in the South East of South Australia which is considered one of the state's most premium sites for cave diving.

Appearing as a small opening in the middle of a farm, the myriad of gothic tunnels that travel for over eight kilometres beneath the surface are surrounded by walls of limestone which attract some of the sport's most curious explorers.

Grant Pearce spends his weekdays studying Groundwater for the Department of Environment, Water and Natural Resources where he works as a scientist and on weekends, he goes cave diving.

"There's no better feeling than discovering a new part of the cave, being the first person to have seen something ever," he said.

Grant is a member of Cave Divers Association Australia and has been cave diving for 25 years.

While there have been instances where he has had to extract some of his friends from the cave who failed to surface, he says there's nothing that will prevent him from diving back down.

"I always go back there because I love it," he laughed.