The origins of Tank Cave's name was a water tank that used to rest right over the top of the entrance. The entrance is underground, after a climbing down a short ladder, the small surface lake leads to an extensive, maze like system with over 7km of diveable passage - this makes it one of the longest underwater caves in Australia. Fixed line runs throughout most of the cave, although many of the side passages do require jumps. Access Requirements : Tank Cave is open on the weekends. Bookings are made through the CDAA website. Contact the booking officer to arrange weekday diving with a minimum of 1 weeks’ notice. An Access Officer is required for each day of diving. The Access Officer is required to open the cave and follow the AO protocols put in place as required. Maximum of 12 divers per day, including the Access Officer.