South Central Kentucky is cave country, and Mammoth is the mother ship. Welcome to the longest known cave on the planet, with 400 miles of mapped and explored passageways. Largely nocturnal mammals – including up to 12 million bats in one section alone – call the chambers home. Tours catering to budding speleologists and leery claustrophobes include spacious jaunts along "Broadway" (a wide underground passage) and intense belly crawls into Mammoth's deep, narrow innards.