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The Mega Cavern is a former limestone mine in Louisville, Kentucky. The cave stretches under parts of the Watterson Expressway and the Louisville Zoo. Due to its support structures, it is classified as a building and is the largest building in Kentucky. The cavern is used for business, storage, recycling, and tourism, with offerings including tram-guided tours, zipline tours, a ropes course, an annual holiday lights display, and, previously, a mountain bike park