This area has the finest cave diving in Australia, with over 40 sites available. One of the finest is Piccaninnie Ponds.
The marvellous photograph below, from the January 1984 issue of National Geographic, catches it perfectly.
Divers can exit the Cathedral through another opening at 25m to swim down to the bottom of the chasm at 57m. At the very bottom of the chasm is the entrance to a tunnel that goes no one knows quite where; though some have died trying to find out. The tunnel is narrow and once in offers few opportunities to turn around. One can only stay at the this level for a few minutes since 57m is almost twice the maximum safe depth for air diving. This video shows a dive down the tunnel.
The real attraction of Piccaninnie Ponds is the remarkable clarity of the water. It is as clear as tap water. Visibility must have been 40m when I was there and gave me the sensation that that I was flying in air. If the dive is done at the right time on a bright sunny day the sunlight illuminates deep into the chasm and creates a magical effect.
There are no technical difficulties and it can be dived with just a single tank rig. I found it an excellent dive and a worthwhile entry in any logbook.