John Ackerman on Caving

Explore the limestone labyrinth

John Ackerman in the upper level of Ackerman’s Cave.

John Ackerman in the upper level of Ackerman’s Cave

photo by Martin Larsen

Growing up in the Twin Cities, John Ackerman would occasionally venture underground with his high school friends. They would spend hours exploring the old mines in St. Paul and Lilydale, and even once trekked down into the sewers (though toxic sewer gases and seemingly fearless rats limited those excursions). Ackerman loved being underground, wandering the labyrinth. A few years later, this urge to explore led him to southern Minnesota, where the limestone had never been scraped off by glaciers and where water had carved vast networks underground. There he discovered what would become his life’s passion: caving, which is exactly as it sounds. You enter a cave with lights, ropes, hard hats, and warm clothes to see what’s down there. Ackerman couldn’t get enough. He kept discovering more new caves, and thanks to his successful furniture restoration business, he started buying land around the cave entrances, as well as the “underground rights.” Throughout Fillmore County (southeast of Rochester) and Iowa, he now owns some 36 miles of caves—which he calls the Minnesota Cave Preserve, and which he plans to preserve for science and exploration. “Caves are like time capsules,” he says. “There’s so much scientific value to them.” His most noteworthy findings include a 27,000-year-old antler from an extinct moose and a saber-toothed cat skull from the same era. Ackerman also established the Minnesota Caving Club, which has no membership fees and leads expeditions to the Minnesota Cave Preserve nearly every weekend. “We discover waterfalls, rivers, formations, fossils, huge rooms, crevices that are 100 feet deep, and multicolored passages from the minerals that leech through the rocks,” he explains. “The terrain is so different in each cave. It’s just a landscape where you never know what you’re going to see around the next corner.” 

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“Go with an organized caving club that can mentor you. If there are tight spots, you could get caught and die in there, or fall 100 feet.”


Hard hat, gloves, sturdy boots, headlamp along with at least two extra waterproof, long-life LED lights. Clothes for 47–48-degree temperatures. Optional: Wet/dry suit


Never disturb bats: They can die easily from using their fat stores. Never touch a formation. Walk around them gently. No drinking or drugs while caving.


Never cave alone or without landowner permission. Dress warmly.


Minnesota Caving Club, Minnesota Speleological Survey


Weekend expeditions hosted by Minnesota Caving Club

Wild Caves:

Southeast Minnesota, Southwest Wisconsin, Northeast Iowa

Tourist Caves:

Mystery Cave, Niagara Cave, Soudan Underground Mine State Park (Minnesota), Crystal Cave, Cave of the Mounds, Eagle Cave (Wisconsin), Jewel Cave National Monument, Wind Cave National Park, Rushmore Cave (South Dakota)


“Some cavers excel at climbing. Some cavers excel at photography. Some cavers excel at surveying.”


Walking rough terrain, over rocks and cracks. Hill climbing. Hole crawling.


“There’s a lot of camaraderie. We’re pretty much like-minded people. We love the outdoors. We love hiking outside looking for caves. And we have people that range from 6 years old to people in their 60s.”


Hypothermia. “Even though you’re dressed properly, once you stop and sit down for two, three, four hours, you start slipping into the early stages of hypothermia. You start shivering, and once your core starts losing heat, it’s hard to get it back.”

High Risk:

Rainfall, snow melt. “We try not to go into caves at all when there is any risk of rain nearby. It can be raining miles and miles away, and sunny where the cave is, and within a matter of hours, that cave could flood to the ceiling. The safest time to go caving in river caves is winter, when there’s no threat of rain.”


“It helps to be physically fit. In many of my caves, I’ve created safe, man-made entrances where you have to climb down a 30-inch hole on a ladder for almost 200 feet.”


Scientists at the University of Minnesota have dated formations in Ackerman’s caves at 114,000 years old.


Caves where no human has ever set foot.


Tourist Caves: *
Wild Caves: ****                                   
Cave Diving (swimming through underwater caves): **********

Digital Extra: Underground Secrets

Check out the tight spaces and on-your-belly tunnels winding through the Minnesota Cave Preserves.