As a boy, he used to squeeze his body into drainage pipes, snaking along to see how far he could go.

As an adult, he made the two top-grossing movies of all time, “Avatar” and “Titanic.”

And on Wednesday, James Cameron folded his 6-foot-2-inch frame into a 43-inch-wide capsule and plummeted, alone, down five miles in the New Britain Trench off Papua New Guinea. His feat, in a 24-foot-long craft dubbed the Deepsea Challenger, broke by a mile the world depth record for modern vehicles that a Japanese submersible had held.

But he wants to go deeper: This month, Mr. Cameron plans to plunge nearly seven miles to the planet’s most inaccessible spot: the Challenger Deep in the western Pacific, an alien world thought to swarm with bizarre eels and worms, fish and crustaceans. He wants to spend six hours among them, filming the creatures and sucking up samples with a slurp gun.

“It’s a blast,” Mr. Cameron said in an interview during sea trials of his new craft. “There’s nothing more fun than getting bolted into this and seeing things that human beings have never seen before. Forget about red carpets and all that glitzy stuff.”