Tour the mines and caves under the surface of Minnesota

Sweat threatened to break beneath my yellow hard hat as I stood in an open-air shelter, the only shade on a sunny hilltop outside the entry to Minnesota's first iron ore mine. Just in time, a door swung open and brought nature's air conditioning with it. That blast of cool air, transported here from a half-mile beneath the Earth's surface, fanned out of a 90-year-old metal-walled cage, trading places with the 10 humans who went in. We were on our way down, 27 stories underground, in the footsteps of the miners who took this cage to work every day, at what is now Soudan Underground Mine State Park.

"It's gonna be fast," our guide said as the doors clanged shut. Then, we dropped.

On the surface, Minnesota is dotted with lakes and furred by forests. In the cities, skyscrapers and cathedrals soar, suburban tracts meander. But if you look past the visible natural and man-made wonders of our state — look beneath them, actually — you'll find a whole other Minnesota underground.

In northern Minnesota, the Iron Range is still home to an active mining industry that has transformed both the cultural and topographical landscape of the region since the late 19th century. In southeastern Minnesota, cave systems that began forming hundreds of millions of years ago are untouched windows into our planet's past.

The two areas couldn't be more different, geologically: The ore deposits Up North are valued for their strength, while the limestone in the south is so soft that flowing water dissolved it into caverns. But both subterranean worlds are road maps to the history of the planet, evidence that the Earth is far greater than anything man can make out of it.

Mines of the Iron Range

The northern landscape is punctured by open pits, some still active, some filled with crystalline water. The lakes are bracketed by red hills of "overburden," leftover dirt denuded of its deposits and reclaimed by greenery. These craters are so plentiful in this region, it feels like you're always at the top of something, like standing at the edge of the Grand Canyon. Visitors curious about mining have a number of options, including tours of a working mine or one that closed in 1978, as well as overlooks of massive man-made canyons.

The almost Tower of Terror-like ride down the mine shaft remains the only way in or out. Lit by a guide's flashlight, our cage zoomed past landings once picked apart by immigrant workers with axes and drills, the mineral-rich rocks they unearthed so sturdy they became cars and refrigerators.

Finally, our cage slowed to a halt 2,341 feet down. Our group exited into a sort of miners' depot, where open-air trains waited to haul passengers, horizontally now, to a preserved work area.

All in all, some 50 miles of tunnels have been carved into this ground. This tour explores just three-fourths of one of those miles.

Like the Seven Dwarfs, we piled into the rail car and took off for a cold and windy ride into the tunnel. Darkness was punctuated only by a few artfully lit miner mannequins; we whipped by these frozen workers so suddenly, they looked eerily real.

Our destination was a winding metal staircase, which we climbed to reach a blasted-out work area, known as a stope. Here, we learned of the workers' plight — how most teams were multilingual so workers couldn't communicate enough to organize; how the miners worked in darkness, their areas lit only by a candle attached to their hard-hats; how the sound of the drills spinning into rock was deafening, and the dust poisonous.

Back at the train station, a walkway leads to another tunnel and a cathedral-size room devoted not to mining but physics. In the 1980s, a team of scientists set up shop down here to study proton decay without the pesky interference of cosmic rays. Today, it's a multipurpose workspace for scientists investigating dark matter, bat habitats and an ancient bacteria that survived for 2.7 billion years in such harsh conditions that it is hypothesized to also be living on Mars. Mind blown.

Caves in the southeast

Many millennia after those bacteria evolved, the Midwest was covered by a shallow sea. Soft limestone rock made of ocean sediment formed, and after that sea dried up, the constant trickling of rain and river water into the limestone eventually made way for underground passages and slimy-looking formations — stalactites and stalagmites — that expand by about the width of a ream of paper every century.

Hundreds of caves root beneath the farms of southeast Minnesota. Their discoveries are often similar. Some pigs go missing or bats fly out of the ground, and a curious farmer follows the trail to find a labyrinth of enclosed corridors, pristine waterways and otherworldly formations.

The state park system has preserved one such labyrinth, Mystery Cave. These 12 miles of underground avenues make up the longest known cave in Minnesota. The Scenic Tour, a one-hour quickie past some of its most elaborate features, is a stunning introduction to its treasures.

In some areas, the distance between the cave ceiling and the ground above us was only 7 feet. But how different it was from the woodsy surface above — almost forty degrees cooler, and magical. Water drizzling down for centuries has deposited minerals that have collected into muddy-looking mounds dropping from the ceiling or climbing up from the ground. Wavy slicks (cave bacon) and fluffy balls (cave popcorn) accentuate the water's artistic power.

It is so tempting to reach out and run your fingers over the cartoonlike rocks. But while heavy machinery scoops up the ground on the Iron Range, down here, we're told not to leave so much as a fingerprint. Oils from our hands could alter the natural flow that's been moving longer than humans have existed.

At the end of a cave hallway, the pavement ends and darkness looms. Beyond that point, only adventurers go; much of a four-hour expedition led by park rangers is crawled on hands and knees. I was intrigued, but too chicken.

Instead, I opted for the Geology Tour, two hours in a different branch of the cave. Another cement entry, unmarked and set back in the woods, was only a five-minute drive from the visitor's center and the Scenic Tour entrance, but underground and by foot, it would take seven hours to shimmy and crawl from one gateway to the other.

This unlit part of the cave lacks the more intricate features that are found in the main entry. Here, the beauty is more subtle: gypsum that lends some walls a glittery shine; fossils of shelled sea creatures that look like Cheerios stamped into the rock.

Sharyn Jackson • 612-673-4853