Decorah Ice Cave State Preserve contains one of the largest caverns containing ice in the Midwest, and is famed due to the rare ice deposits inside of it until late summer. The cave itself was formed in 450-million-year-old limestone and dolomite.
The ice formation is created when the chilly air of winter enters the cave and lowers the rock wall temperature. When spring thaw occurs, surface water seeps into the cave and freezes upon contact with the still-cold walls, and reaches maximum thickness in June. Fall usually sees the cave free of ice, which doesn't return until the following spring.
A steep flight of stairs leads to the cave entrance, which is east of the parking area. Visitors are asked to use caution, as the inside of the cave gradually slopes and there is usually ice present on the walls and floor. Visitors are also cautioned not to disturb any loose rocks inside the cavern.
The preserve is located in the Barbara Barnhard VanPeenen Memorial Park and was given to the Decorah City Parks Commission in 1954. It became a geological state preserve in 1973.
Currently the Ice Cave is blocked-off 10 feet into the cavern due to safety concerns.