Sanctum (2011)

This is an okay Australian movie based on a true story. Frank McGuire (Richard Roxburgh), the leading expert on underwater caves has taken a team to the Esa'ala Cave in Papua New Guinea, one of the few unexplored areas left on Earth. His 17-year-old son Josh (Rhys Wakefield) also joins the expedition. Frank and another diver decide to explore an area known as Devil's Restriction, when her oxygen hose snaps, she drowns. Then a storm hits and starts flooding the cave, forcing the remaining survivors to search for an alternative path to the surface.

I enjoyed the interaction between the father and son. Stunt diver Agnes Milowka drowned in a cave on February 27, 2011 after the film had been released, when she reportedly ran out of air. The story is based on the experience of co-producer Andrew Wight. He was exploring a remote cave system underneath the Nullarbor Plain in Australia when a storm hit and they had to find a different path out. Miraculously, all fourteen members survived. A large tank was used for most of the underwater scenes. The entrance to the fictional cave is modeled after the Cave of Swallows in Mexico and the Nare cave in Papua New Guinea.