See Inside a Cave in Illinois that Was Closed Because of Bats
It's the only cave in Illinois that's open to the public, but it wasn't open for a long time. That's because of a danger that involved bats. Now, it's available to explore again, but there's a catch.
Kudos to Only In Your State for bringing Illinois Caverns up in a recent article. This interesting place has quite a history that dates back to 1901 when it was located on a farm as documented by the Illinois Department of Natural Resources. Back in those days, visitors would be taken to the cave via horse-drawn wagon.
Illinois Caverns ended up being closed for quite some time due to a fungi that was found on the bats within its walls. Officials were concerned that the public would unintentionally end up transmitting that outside of the cave ecosystem. The cave would eventually reopen in 2021, but that's conditional. Visitors are required to be at least a party of 4 and everyone must wear hard hats.
Illinois Caverns is located just south of St. Louis in Waterloo, Illinois. It's a relatively short drive from the tri-state area that provides a very natural cave experience. According to the official website, over 6 miles of the cave system have been explored and documented, but there is still more that awaits adventurers under Illinois.