There’s an underwater mini-volcano of sorts – a conical vent that spurts steaming hot water – at the bottom of a waterway in northern Iceland. I had heard about the geological anomaly on a trip to the island nation in 2009. A decade later, I found myself zipped to the nostrils in neoprene, riding a little dinghy out to sea as it battled the howling arctic wind.

I had spent years touring the world’s legendary reefs as a scuba professional, but rumors of an actual portal to the center of the Earth had never left my imagination. I bit the mouthpiece of my regulator with anticipation. My guide cut the engines when we reached the middle of the fjord – we rolled ourselves backward off the bow and slid below the waves. Within seconds, the surface disappeared, the rays of sunshine blocked by the turbid, icy water. Blindly, we descended, following a thin tether that led the way through the blackness.

I almost didn’t resurface.

My dry suit malfunctioned – I couldn’t get enough air into the apparatus – and as we continued downward, the accumulating atmospheres of pressure began to crush my body like a python’’s strangle. Had I been a novice diver, I would have shot 100 feet to the surface, gotten the bends and, without a decompression chamber nearby, probably died. Instead, I quieted my instincts, calmed my harried breathing and motioned to my guide, who helped me fix the blockage in my gear.

Then we lingered a bit, orbiting the submarine chimney. The frigid waters were weirdly warm as we approached the vent’s opening. Only our beams allowed us to decipher the vague shapes of this pale, muted realm. Wolffish flashed their gnarled teeth at my flashlight’s muted glow. My mind began to wander – perhaps we were being watched by other creatures as we made another ring around the small volcano. There was whale song all around.

I haven’t returned to the water since that near-fatal dive in Iceland. But the memory has resurfaced with news of the Titan vessel and its five passengers believed to be dead by this deadline. It has sparked wide attention and obsession. The mystery. The hubris. The money. The Michael Crichton-esque fantasy of a possible recovery. And the legend of the Titanic, which, a hundred-plus years on, still finds its way into our everyday conversations.

For as long as I can remember, I’ve had conflicting feelings about the sea. When I started diving professionally, I found something mirthful about exploring the shallows. The shining sun of the tropics – the usual setting for my underwater excursions – easily pierced the blue.

But the lower depths of the ocean felt different. They spooked me. It’s the closest thing we have to an alien world – a hostile place requiring much more than the armor of a dry suit.

To visit the ocean floor, thousands of feet beyond the limits of recreational diving, one must be encased in metal to stave off the instant pulverization of a hundred atmospheres. The vessels capable of braving the journey are largely windowless, with just one small, opaque porthole and an external light that casts a hazy beam into the murk. Not that the view matters, because the color spectrum fades to gray as deep water curbs the wavelengths of light.

I wondered whether such expeditions are rooted in the same desire for bragging rights shared by the spate of passengers launching into space. But space is different – it’s as empty as it is infinite. We stare up at the stars in awe.

The oceans, however, are our past.

The felled ship, once touted as the world’s greatest, has remained a parable for nature’s power over the mightiest efforts of humankind to assert its dominance over the planet.

My 15-minute mishap in the waters of Iceland felt like an eternity and still fills me with dread. But to grasp the hours passing at the bottom of the Atlantic Ocean feels as impossible as bending one’s mind around the infinite vastness of our planet’s primal depths.

Brandon Presser is the author of “The Far Land: 200 Years of Murder, Mania, and Mutiny in the South Pacific” and contributes to The Washington Post.