Illinois Caverns will be open seasonally from April 15th through October 31st. Weekly, the site will be open Thursday through Sunday from 8 AM to 4 PM with the cave itself being open from 9-3.

There is no admission charge, but guests are required to complete an application permit at the site office before entering the cave. Visitors are required to be in groups of four or more, have sturdy boots, a hard hat and three sources of light per person.

Illinois Caverns State Natural Area is a 120-acre preserve owned by the Illinois Department of Natural Resources. The main attraction of the site is an uninmproved wild cave with nearly three miles of walking-height passage. Located in karst-rich Monroe County, the area contains fields, woodlands, native grasses and a half-mile long prairie trail.

Illinois Caverns contains an extensive array of spectacular cave formations, including stalactites, stalagmites, rimstones dams, flowstone, and soda straws. Many of the formations are actively growing with the continued deposition of calcium carbonate. An underground stream meanders through the cave in its enriched bed. Throughout the year, the temperature in the cave remains a relatively constant 58 degrees Fahrenheit. Approximately 6 miles of the cavern's passages have been mapped by a caving group from Chicago, the windy City Grotto.

Over millenniums of time, the dissolving action of water along the subterranean cracks formed large, water-filled conduits or underground streams. Meanwhile, erosion on the surface began to cut valleys into the surrounding countryside. As the surface valleys deepened, some of the underground passages were drained, creating the air-filled passages known as caves.

During the cave-making process, water acts not only as a dissolver, but also as a builder. In the protected cave environment, dripping and seeping water can deposit carbonate materials and from a host of geological formations.