Hollywood director James Cameron has returned to the surface after plunging nearly 11km (seven miles) down to the deepest place in the ocean, the Mariana Trench in the western Pacific.
He made the solo descent in a submarine called Deepsea Challenger, taking over two hours to reach the bottom.
He spent more than four hours exploring the ocean floor, before a speedy ascent back to the surface.
His craft was kitted out with cameras so he could film the deep in 3D.
"It was absolutely the most remote, isolated place on the planet," Mr Cameron told BBC News.
"I really feel like in one day I've been to another planet and come back."
This is only the second manned expedition to the ocean's deepest depths - the first took place in 1960 when US Navy Lt Don Walsh and Swiss oceanographer Jacques Piccard spent about 20 minutes on the ocean floor in a bathyscaphe called the Trieste.
Lt Walsh, who is now in his 80s, joined Mr Cameron and his team of engineers out at sea for the dive.
"It did bring back a lot of memories, just being out there and remembering what we did there," he told BBC News. "It was really grand."
Mr Cameron has spent the past few years working in secret with his team of engineers to design and build the craft, which weighs 11 tonnes and is more than 7m (23ft) long.
He describes it as a "vertical torpedo" that slices through the water allowing him a speedy descent.
The extraordinary attention to detail prevented him from suffering from too much nervousness.
"I can't say that I wasn't apprehensive in the last few days and even the weeks leading up to this, but there's another part of my mind that really understands the engineering and knows why we did everything the way we did," he said.
"Any apprehension I had I left at the hatch. When I went into the sub, I was all pilot at that point."
The tiny compartment that the film-maker sits in is made from thick steel, which is able to resist the 1,000 atmospheres of pressure he experienced at full ocean depth.
The rest of the vertical column is made from a material called syntactic foam - a solid made mostly of hollow "microballoons" - giving it enough buoyancy to float back up.
The sub has so many lights and cameras that it is like an underwater TV studio - with Mr Cameron able to direct and film the action from within. He intends to release a documentary.
It also has robotic arms, allowing him to collect samples of rocks and soils, and a team of researchers are working alongside the director to identify any new species. He says that science is key to his mission.
But the first task was to get to the inky depths - which despite untold hours of training, still surprised Mr Cameron.
"My reference frame was going to the Titanic 10 or 12 years ago, and thinking that was the deepest place I could ever imagine," he recalled.
"On this dive I blazed past Titanic depth at 12,000 ft and was only a third of the way down, and the numbers keep going up and up and up on the depth gauge.
"You just kind of look at them with a sense of disbelief, and you wonder if the bottom is ever going to be there."
At the bottom, Mr Cameron encountered incredibly fine silt, which he had to be careful not to disturb. He said he spotted a few small, as-yet unidentified life forms but found the depths to