Gearing up on the platform for my last dive of the trip, I peer into the electric-blue water trying to visualize the winding path we plan to follow as Scott “Bear” Fritz, my fast-talking dive guide, fires off directions. “We’ll drop down this pillar here,” he gestures with his right hand. “At about 80 feet you’ll see a small opening. That’s the Secret Tunnel. It’s off the regular dive path, but it’ll get us to the Lake Room in a matter of minutes. From there we’ll follow the wall to the tar boat, go up a set of ladders through Clinton Shaft, follow the railroad ties into the Grand Canyon Bowl and loop back around into the Lake Room.” “Pheew,” I think, “OK, I’ve got it…maybe.” But then he starts talking again, “Then we’ll turn and swim through the Rope Room, pass through the Trail 3 slit into the 1095 Bowl and we’re back to the dock.” My mouth hangs open slightly. “Tell you what,” I say. “I’ll just stay right behind you.”

It’s a good choice. There’s no better guide to Missouri’s Bonne Terre Mine. Fritz has been diving the mine for more than 20 years, and he’s the training director who makes sure all the mine’s dive guides are fully prepared to take tourists or students into this underwater maze. There are more that 50 planned trails open to the public that the guides must know like the backs of their hands. Though, under special circumstances, exploratory dives are possible here as well. Dubbed “Bear” trails, these more advanced dives, lead by the eponymous guide himself, delve into the unlit and underexplored sections of the mine. But Bear Trails, like the one I’m about to dive, are only for divers who prove they’ve got the scuba skills and the air consumption to do them, and once we drop down the aforementioned pillar and enter the Secret Tunnel, I understand why.

We slide one-by-one into the narrow, square-cut shaft under a hundred feet of rock. Along the floor, a pair of metal ore-cart tracks stretches past the edges of our high beams. It’s easy to imagine men in this tunnel, urging stubborn mules hitched to ore carts, lugging load after endless load to the edge of this shaft, tipping the cart over the lip, sending a shower of ore into the bowels of the machine. But imagination time doesn’t last long. When we emerge on the other side, we’re in an unlit chamber, a cavernous void that swallows the beam of my light, and I focus on the bottom to maintain a point of reference until we reach the opposite end, and yet another square-shaped passage. This one is wider than the last, and we swim side-by-side until we arrive at Clinton Shaft, a system of round, tight tunnels, angling different directions as they traverse upward through multiple levels, with fragile wooden ladders leading from one hole to the next. Bear points his hand-mounted light into the narrow shaft and motions me forward. “Here we go,” I say to myself as I fin carefully up the length of the ladders, following, in the still silence, the footsteps of men who lived and died to create this labyrinth in the name of industry.

This is the lure of what the Bonne Terre crew has dubbed “deep earth diving,” a seemingly endless underground world, frozen in time. Fritz openly admits he has “the fever,” a driving desire to explore, to see what’s down the next tunnel, that has kept him coming back for more than two decades. Pillars, shafts, sheer walls and ceilings—hewn entirely by human hands—stretch for miles in all directions, leaving a sprawling, five-level catacomb beneath the town, and at every underwater turn all manner of artifacts—shovels, rock drills, ore carts and blasting caps—lay strewn across the landscape, as if the workers who left them simply went home at the blow of the foreman’s whistle and never returned to clean up after themselves. Of course, back in the day, the mine’s deepest reaches were not underwater. A massive pump system stemmed the flow of encroaching groundwater as the miners pushed ever deeper. But when this, the world’s largest lead mine, was all mined out, the men retreated, the pumps were turned off and the water trickled in to fill the void. These days, mine owners Doug and Cathy Georgens have turned the pumps back on, but it was never their intention to drain the mine completely, just enough to keep the water level constant and provide divers with access to their unique underwater vision.

And a big part of what makes that vision possible is light. The electric blue of the water is a product of the 500,000 watts of high-powered stadium lighting that the Georgens and their team have strung from pillar to pillar, through hundreds of feet of subterranean air space. The crystal-clear, rock-filtered water is clean enough to drink, and the long, blue waves of light that penetrate to the darkest depths of the motionless, billion-gallon lake lend an almost Caribbean illusion. But that illusion disperses as fast as your body heat when you make that first giant stride. Bonne Terre’s dive deck hovers on the water’s surface a full 150 feet into the earth, and though it’s a short walk down from the small shed that covers the mine’s only opening, the environmental change is complete. From the searing Missouri summer heat, it’s like entering the world’s largest walk-in refrigerator, where the air stays a constant 62 degrees, the water a brisk 58, year round.
Of course, those temps sound pretty good during the winter, which is Bonne Terre’s high season. Here in the Midwest, regional dive shops are short on spots to take Open-Water classes, especially when the quarry temperatures dip below freezing. So Bonne Terre Mine’s constant conditions provide year-round diving opportunities for students and divers who don’t have the time, money or desire to go coastal. But the mine has also attracted higher-profile attention. In 1983, Jacques Cousteau’s film team came to document the dramatic underwater scenery, in April 2000, “National Geographic Adventure” named the diving at Bonne Terre Mine one of the top 10 adventures in America, and over the years, a handful of documentaries have been filmed here and shown on the Discovery and History channels.

For everyday divers, the diving experience at Bonne Terre is very accessible. The town of Bonne Terre, Mo., is about an hour’s drive south of St. Louis. The dive operation is only open on weekends, and there are on-site accommodation options. The diving itself is totally safe because it is highly controlled—a necessary precaution in a place with innumerable overhead tunnels that can easily swallow even an experienced diver who doesn’t know his or her way around. Every group of divers has a guide and a safety diver, and every diver’s first visit to the mine starts with a checkout dive, no matter what their experience level. Visitors to the mine dive the 24 trails in sequence—they get a bit a harder as the numbers get larger—so if you make it through Trail 6 your first weekend, you’ll start at Trail 7 on your next visit. Dive lights are not allowed or necessary on the guided tours.

As for me, following Fritz around for a weekend proves a very tempting taste of what the mine has to offer. As we exit Clinton Shaft, I stay right on Fritz’s fin straps through the winding path back to the dock. Like an enthusiastic newbie, I turn my head in all directions—from rock walls and narrow passageways, to discarded drill bits and shovels—trying to take it all in, but at one point, we swim onto a ledge and Fritz stops me short. He puts his hand on my shoulder and points out into what looks like open water. Then he kicks his fins out in front of him, leans back and sits down on a rock like a man settling into his favorite easy chair. He looks over at me and spreads his arms wide. By this time, my eyes have focused, and I see pillar after pillar stretching out into the soft light like a massive forest marching into the distance; I settle down beside him to admire the scene. “That’s my favorite spot, where I go to relax” Fritz says when we climb out of the water. “We call it the Redwood Forest.” I nod my head in agreement, looking back over my shoulder at the water. Fritz laughs, “Looks like you’re getting the fever,” he says. “You’ll be back.”

Download Shortened Version Published in Scuba Diving magazine