Mystery Cave

Mystery Cave is the longest cave in Minnesota, with over 13 miles of passage developed in two separate rock layers, and volunteers are still resurveying and remapping it.

It sits in the Driftless Area, the region the last ice sheets went around rather than over, which is why the surface here is karst: sinkholes, disappearing streams and caves, instead of the flat glacial till that covers most of the state.

The rock was deposited about 450 million years ago, as shallow seas repeatedly advanced across the land and retreated again. Alternating layers of mud and marine debris were compressed into limestone, shale and sandstone, and those beds now sit around 1,300 feet above sea level. The cave itself is far younger. Within the last 500,000 to a million years, floodwater dissolved along fractures in the limestone to open out most of the passage. Inside are stalactites, stalagmites and underground pools, at a constant 48 degrees Fahrenheit.

The cave is one half of Forestville Mystery Cave State Park, and the other half is a village. Forestville has been restored to its nineteenth century appearance and is run as a historic site by the Minnesota Historical Society, about five miles from the cave. The park covers roughly 3,170 acres with camping, hiking, horse and cross-country ski trails, and cold water streams with genuinely good trout fishing.

Cave tours are guided and ticketed, and the park lies between Spring Valley and Preston in the southeast corner of the state.

Above ground the same acidic rainwater has worked on the surface, leaving thousands of sinkholes across the surrounding county. The park holds glacial snails and timber rattlesnakes alongside the ordinary deer, beaver, mink and fox, at least 175 recorded bird species, and brown, brook and rainbow trout in the South Branch of the Root River.

Historic Forestville is run as a living museum set in 1899, with costumed interpreters working the general store, the house, the kitchen, the farm and the barn. The real village was a rural trade centre that went into decline after 1868, when the railway was built somewhere else. By 1889 Felix Meighen, the son of one of its founders, owned the entire village, and the remaining residents worked for him.