They’ve been at it more than a month and have found a promising passage. The goal of the expedition is to chart the maze of tunnels and find the one that exits onto the sea.

“There are no rescues down here - only body recoveries,” Frank reminds those who want to stay put and await help. “He’s like the most respected explorer of our time ‒ like Columbus, Neil Armstrong,” a diver tells Josh. Still, you can’t help wincing at the comic-book balloons passing for dialogue, some of it describing Frank, the rest delivered by him. Much of this we’ve experience before, only wrapped in sci-fi clichés. Waiting at the bottom are Frank (Richard Roxburgh), the hard-ass team leader as well as Josh’s father, and a four-member crew, nearing exhaustion and already making stupid mistakes.

You have your choice of ways down ‒ rappel or, like hotdog Carl, parachute in. Once there, we’re not disappointed: Esa’ala is a gargantuan sinkhole, the mother of all bathtub drains. A U.S.-Australian co-production ‒ which explains all those Aussie accents ‒ “Sanctum” opens at full tilt like “Jurassic Park.” A whooshing helicopter ferries Carl (Ioan Gruffudd), the corporate head of the expedition, Carl’s girlfriend Victoria (Alice Parkinson), and a teenager named Josh (Rhys Wakefield) to base camp.

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