Cave of the Mounds
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The Cave of the Mounds is a natural limestone cave located in Blue Mounds, Wisconsin, USA. It was discovered by accident on August 4, 1939 when blasting in a limestone quarry revealed a cavern over 20 feet high. It was opened to the public in May of 1940 and has now seen millions of visitors.[citation needed] Known for the quantity and variety of its speleothems, it was named a National Natural Landmark by the Department of the Interior and National Park Service in 1988.