As a kid, John Ackerman wandered tunnels beneath St. Paul, Minnesota, that used to belong to a sand mine; his passion for caves never left him. Now, he's Minnesota's biggest cave collector, and perhaps America's, too, the New York Times reports in a profile. When he's not exploring Minnesota's subterranean world, Ackerman works as a furniture repairman, a business he started in his garage. Now, it's big enough to fund his cave habit—which can be pretty pricey.
Once Ackerman has found a sinkhole, he excavates accumulated sediment; then, he climbs in. Using special wave signals and an underground camera, he and a partner identify cave passages. When a cave has been found, Ackerman asks the landowner if he can buy it, "and (the landowner is) going to say, ‘Why would I want to sell you one acre or 10 acres in the middle of my property?'" One reason: He'll pay tens of thousands per acre, the Times notes. But it's not just landowners that get fed up with Ackerman: Minnesota land officials aren't always pleased with his work. "But I’ve constantly reminded them I’m protecting them and I’m allowing scientists to study them," he says. Click for the full story. (Read more Minnesota stories.)