Marengo Cave was a refuge when a deadly tornado blew through town in May 2004, thus finally fulfilling its role as a fallout shelter, although the fallout was from trees, not atom bombs.
This cave has expanded outside of natural confines for tourist appeal. It now offers "The Crawl" and "The Bat" as attractions. Navigating through The Crawl is like slithering through a giant intestine, and is intended to give one the sensation of cave exploration without the cold, the wet, etc. -- just the claustrophobia. No shoes are allowed in The Crawl. It's only a few feet from the snack bar.
The Bat is a wood tower uphill and a metal tower downhill, between which is stretched a metal wire. People slide along it, pretending to be bats.
The cave itself still has its share of subterranean wonders, such as the Crystal Palace Room where nature is improved with piped in music and flashing colored lights.