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Spring Valley Caverns

(credit: AIZAR RALDES/AFP/Getty Images)

Minn. Man’s Cave Collection Is His Hobby, Passion

John Ackerman is a big-time landlord of subterranean real estate. Ackerman, 59, owns Spring Valley Caverns, the largest private cave in Minnesota but just the beginning of his underground empire, which he calls the Minnesota Cave Preserve.

11/07/2013