When you go underwater in a submersible, sunlight blinks through the waves that lap against the viewport. This part doesn’t last long. Soon, as the sub begins to descend, the sunlight starts to fade into blue, and as the sub goes down deeper, every color other than blue begins to drain away. Before long, water will start to look dark cobalt. A few hundred feet below the water’s surface, that blue becomes grayish indigo. When author Susan Casey went on her first dive, she described the color—the only light wavelength with enough energy to penetrate at such depth, a “pure ultramarine”—as narcotic. Another thousand feet, and it becomes pitch black.
In the twilight zone, the first layer of ocean classed as the deep sea, sunlight is almost nonexistent. A sub’s LED lights shine out onto a strange world. Half of the species are older than the dinosaurs. Gill sharks, which have existed on Earth for almost 400 million years, swim by. Once a submersible reaches a certain depth, there are no red-light waves, so the fish are bright red—which renders them invisible—or they’re white. Sometimes they’re shiny, like floating mirrors. In many cases, the shape of the creatures and the way they move defies any existing notion of what an animal looks like.
“Why have we ignored so much of the deep for so long? It’s as if we live in a mansion filled with treasures and artworks and fabulous animals, but haven’t bothered to look in most of the rooms,” Casey wrote in her August 2023 book, The Underworld: Journeys to the Depths of the Ocean. “It’s a failure of curiosity, to say the least, a hobbling myopia that leaves us oddly unacquainted with our own home.”
The deep sea is an ecosystem that, by volume, dominates the planet, but to most people, it’s almost entirely inaccessible because so few vessels that are equipped for exploration accept passengers. The deeper you go, the more inaccessible the ocean is; fewer people have reached the absolute nadir than have flown to the International Space Station. Vessels that can reach the deep sea are almost entirely either used for commercial purposes (the oil industry uses subs to maintain underwater wells and pipelines), scientific research, or they’re luxury craft manufactured for the wealthy. To the degree that deep-sea tourism companies exist, they have offered something that operates largely outside of clear legal jurisdiction, making it incumbent on travelers to assess a company’s safety standards and their own taste for risk.
For those who make the descent, though, the experience can be cathartic, rearranging the perception of what the world is made of in ways that are often compared to an astronaut’s experience of seeing Earth from space. The deep sea is as alien as space but closer, stranger than the moon but belonging to this planet. “It is not space. It’s completely alive,” Casey tells me. “When you think of how much emphasis culturally we put on the idea of exploration in space, and here we have this inner space that’s just a matrix of life. That, to me, is very moving. It really expands your perspective on Earth.”
Deep-sea exploration has always been rare. The first functional submarine was likely developed by Cornelius Drebbel in the 17th century, to navigate under the Thames in London, but it wasn’t until three centuries later that the technology was substantially expanded for military and scientific use. Submarines and submersibles—the difference being that the latter usually have to be transported over long distances on another ship or vessel and operate mostly to descend—were always closely tied to exploration, but it wasn’t until 1960 that explorers finally reached the deepest point of the ocean. They used a bathyscaphe, a kind of submersible, and went down to the bottom of Mariana Trench, more than 35,000 feet below the ocean’s surface. The feat wasn’t replicated until 2012, when film director James Cameron descended in a submersible called the Deepsea Challenger.
Since then, though, there have been 20 more crewed descents to the bottom of the Mariana Trench, including explorer Victor Vescovo’s Five Deeps Expedition, which saw him dive to the deepest location in all five of the world’s oceans between December 2018 and September 2019. While the trench remains out of reach for most, private sub experiences are available to almost any committed and affluent traveler, and there are innumerable efforts to make the sea accessible by creative and novel means. In 2019, Uber launched a submersible rideshare to explore the Great Barrier Reef. One company in Vietnam offers submersible trips for 24 people at a time to a few hundred feet underneath the ocean’s surface, and a smattering of other companies offer 100-foot-deep submarine trips in places like Hawai‘i and Cozumel, Mexico.
None of these reach the deep sea, considered to begin at deeper than 600 feet, or even really come close to it. In some cases, they might be more readily compared to scuba diving (scuba divers can’t go beyond 120 feet or so below sea surface). After the twilight zone, at around 3,300 feet, the ocean becomes completely dark, referred to as the midnight zone, and after 13,100 feet it is considered the abyssal zone. If reaching the deep sea is distinct, reaching the twilight zone can be an introduction to an alien world. “I call it the Manhattan of the deep because it’s just filled with life,” Casey says. “It has more marine creatures in it than all the other regions of the ocean combined, and about 80 percent of them can be bioluminescent. It’s this flashing, twinkling, cosmopolis of creatures.”
But there are few options to reach the twilight zone as a traveler. There’s Scott Waters, who owns a submarine company in Tenerife, Spain, and who will bring people who donate to scientific endeavors down to the depths. Waters partners with the Spanish Oceanographic Institution in the Canary Islands and can cater trips according to project and price—a dive off the shore of Tenerife to do microplastics studies costs roughly $1,955, and more expensive trips, like to study climate change in Antarctica or the origins of life at hydrothermal vents, can go up to $54,000. (Says Waters: “The people who want to travel in a submarine are adventurers and explorers who want to make a true impact on science.”) There’s an unconventional pilot in Honduras named Karl Stanley who built his own sub and will take people to a depth of around 2,000 feet. There’s the option of purchasing a private submersible from Triton Submarines, based in Florida, or Norwegian company U-Boat Worx and storing it on a yacht between uses. Then there was OceanGate, which stopped operations after its fatal implosion on a trip to the Titanic wreck in June 2023 with executive Stockton Rush and four passengers onboard.
Before its submersible disappeared, OceanGate was arguably the most high-profile deep-sea tourism company, renowned for its novel technology and Rush’s approach to innovation. The community of submersible enthusiasts is tight-knit, though, and they worried about such a disaster even before investigators announced that the missing craft likely imploded. Stanley raised concerns about OceanGate’s technology after he descended with Rush in 2018, and, as reported by Vanity Fair, The New Yorker, and CNN, several other experts sounded alarms before the incident.
The problem, according to Patrick Lahey, who cofounded Triton Submarines, was that Rush refused to submit OceanGate submersibles to classification. There are a handful of independent, international marine classification companies that audit and ensure a vessel’s safety for its intended depths, including societies like Det Norske Veritas (DNV) that inspected and certified Vescovo’s sub. Getting a sub certified, or classed, is an arduous process that usually involves submitting a vessel to multiple tests in pressure chambers and on descents to depths beyond what it will visit. Because of the details involved, and the fact that there is limited infrastructure for conducting some of the tests (the only pressure chamber big enough to test Vescovo’s sub was in Russia), the process can get expensive quickly. Maintaining classification also takes repeated tests over time; it’s not enough to get classed once.
Strictly speaking, most submersibles don’t fall under classical maritime law since they don’t sail in and out of port—they’re carried on another ship. That means that they’re subject to the laws of the jurisdiction where they operate, which gets murky once they’re 12 miles away from coast in international waters. Insurance companies usually decline to back vessels that aren’t independently classed, but it’s still largely an optional step. For subs that are classed, that undergo the extensive testing and regular review, there is an exceedingly solid track record. “The safety protocols are inviolable. They are sacrosanct,” Casey says. “They’re the center of everything and always have been.”
Many submarines are made of steel, including Stanley’s, or more often, titanium. They can either have a single or double hull, they contain ballast tanks that use water and air to control their buoyancy, and they’re often shaped in a circular or cylindrical shape that best distributes pressure over the entire structure. Subs that are designed to reach the bottom of the ocean have to withstand pressures that reach 15,750 pounds per square inch (PSI); the pressure at sea level is 14.7 PSI. “They really are, to me, magical machines,” says Lahey, who built the titanium submersible that carried Vescovo to the deepest points of all five oceans.
But OceanGate was using a new technology, a carbon fiber hull. The company also said its technology was so advanced and its safety precautions were so assiduous that it exceeded the requirements of any certification process. “The OceanGate sub was an experimental craft, it was an aberration. It did not go through peer review,” says Lahey, who has built two dozen craft for private owners, ranging in price from $2 million to $50 million, and who says he considers submarines to be one of the safest types of vehicle. “We need to insist on certification as a requirement for continued human occupied exploration in the deep sea. I hate the idea that people will be afraid to dive in a sub because of that aberration.”
Like many adventurers, travelers who make the descent to the deep sea have to extend their trust to the systems supporting them. The OceanGate disaster may have showed the cost of exercising that trust on an unproven vessel, but without many rules or regulations in place to govern deep sea tourism, those who want to experience the depths have to use their judgment. Waters’s and Lahey’s subs are classed, as are any submersibles operating within U.S. jurisdiction, for example. But Stanley, who has operated hundreds of dives safely, does not have classification. He tells me he didn’t seek certification because it would have tripled the cost of building his sub. “But I mean, there’s doing things with a bit of common sense and testing and due diligence and having a track record,” he says.
Stanley’s Idabel sub launches from Roatán, an island in Honduras. Idabel is Stanley’s second sub; he began building his first when he was 15 years old, in his parents’ backyard in New Jersey. He brought the sub with him to college in Florida, and after graduation he showed it at a dive show where he met the owner of a resort in Honduras who convinced him to start taking tourists under the water. In the two decades since then, he has dived more than 2,500 times, often transporting three or four people to the deep sea for $1,200 per hour, on trips that last around four hours.
When he was starting out, Stanley told me his passengers were mostly scuba divers who wanted to go deeper than they had been before. Now, it’s engineers at Google and Facebook with disposable incomes who want to experience something rare. “If you have the ability to see with your own eyes the most stable, largest ecosystem on our planet that makes up 90 percent of the living space on the whole Earth, why wouldn’t you?” Stanley said.
A few weeks after the OceanGate disaster, a YouTube travel vlogger with around 482,000 subscribers named Ace visited Stanley in Honduras to go underwater. He filmed himself descending, sitting with a view out the bulbous window. In the video, he chats with Stanley, asking questions about the sub. He gives a shout out to his family. He listens to Stanley’s stories about the longest times spent underwater. At one of the deepest points of the dive, as the sub floats over a neon-studded rock formation, he ogles the strangeness of the view. “Wow. Wow. That’s amazing. Wow. Beautiful,” he says. And then they’re quiet for a few seconds, lingering over the deep.