Blasted open by accident in a limestone quarry in 1939, and so obviously extraordinary that the quarry shut down for good the same year to protect it. A National Natural Landmark, and the best-decorated cave in the upper Midwest: stalactites, flowstone, helictites and pools, in rock about 400 million years old. PUBLIC guided tours year round, Blue Mounds.
Other places on the map within a couple of hours.
