Address: 119 E Main St., Horse Cave, Ky. Once the site of severe contamination with untreated sewage and trash, Hidden River Cave used to be one of the most polluted underground sites in America.

Mammoth Onyx Cave. County: Hart. Address: 3700 L&N Turnpike Road, Horse Cave, Ky. This cave is part of Kentucky Down Under Adventure Zoo, located in Horse Cave.The cave was discovered in 1799 but ...