In 1963, the Texas Highway Department were drilling through rock to test if it could support an overpass in Georgetown, just north of Austin. When their drill bit dropped suddenly, they realised they'd stumbled across a vast subterranean network of karst caves. Now known as the Inner Space Cavern, the chambers are open to visitors, who are wowed by the sharp stalagmites, still pools and even coral (this was once the ocean floor).

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Terrific Texas: 40 Unmissable Things To Do In The Lone Star State