WASHINGTON — In James Cameron’s fantasy films, like “Avatar” and “The Abyss,” the unexplored is splashed in color and fraught with alien danger. But on his dive to the deepest place on Earth, reality proved far different: white, barren and bland.

Yet otherworldly — and amazing.

“I felt like I literally, in the space of one day, had gone to another planet and come back,” Cameron said Monday after returning from the cold, dark place in the western Pacific Ocean, seven miles below the surface. “It was a very surreal day.”

Cameron is the first person to explore the deepest valley in the ocean since two men made a 20-minute foray there more than half a century ago. He spent about three hours gliding through the icy darkness, illuminated only by special lights on the one-man sub he helped design. That was only about half as long as planned because his battery ran low.

This deepest section of the 1,500-mile-long Mariana Trench is so untouched that at first it appeared dull. But there’s something oddly dark and compelling about the first snippets of video that Cameron shot. It’s not what you see, but where it puts you. There is a sense of aloneness that Cameron conveys in the wordless video showing his sub gliding across what he calls “the very soft, almost gelatinous flat plain.”

“My feeling was one of complete isolation from all of humanity,” Cameron said.

It may not have looked all that dramatic and, in a way, Cameron was “doing exploration with training wheels,” said Andy Bowen, who heads the deep submergence lab at Woods Hole Oceanographic Institution.

But it was an amazing start.

The images “do lack the visual impact of highly colorized 3D spectacular representations of the ocean,” Bowen said. But there are still “dramatic discoveries to be made.”

The minute-long snippet, released by trip sponsor National Geographic, is just a coming attraction. Cameron will keep diving in the area, some 200 miles southwest of the island of Guam, where the depth of the trench is called Challenger Deep. And he’s already filming it in 3D for later viewing.

To Cameron, the main thing was to appreciate just being there. He didn’t do that when he first dove to the wreck of the Titanic, and Apollo astronauts have said they never had time to savor where they were.

“There had to be a moment where I just stopped, and took it in, and said, ‘This is where I am; I’m at the bottom of the ocean, the deepest place on Earth. What does that mean?’ ” Cameron told reporters during a conference call.

“I just sat there looking out the window, looking at this barren, desolate lunar plain, appreciating,” Cameron said.

He also realized how alone he was, with that much water above him.

“It’s really the sense of isolation, more than anything, realizing how tiny you are down in this big, vast, black, unknown and unexplored place,” the “Titanic” director said.

He didn’t see tracks of small primitive sea animals on the ocean floor, as he did when he dove more than five miles down several weeks ago. All he saw was voracious shrimp-like critters no bigger than an inch. In future missions, Cameron plans to bring “bait” — like chicken — to set out.

Cameron said the mission was all about exploration, science and discovery. He is the only person to dive there solo, using a lime-green sub called Deepsea Challenger. He is the first person to reach that depth — 35,576 feet — since it was explored in 1960.

While Cameron’s dive was far longer than that of Navy Capt. Don Walsh and Swiss engineer Jacques Piccard 52 years ago, he didn’t reach the trench walls because he was running low on battery power. He said he would return, as would the sub’s Australian co-designer, Ron Allum.