Colossal Cavern

Colossal Cavern is a cave in Kentucky, United States, the main entrance of which is at the foot of a steep hill beyond Eaton Valley, and 1.5 miles from Mammoth Cave. It is connected with what has long been known as the Bedquilt Cave. Several entrances found by local explorers were rough and difficult. They were closed when the property was bought in 1896 by the Louisville & Nashville railway and a new approach made. From the surface to the floor is 240 feet (73 m) under Chester Sandstone and in the St. Louis Limestone. Fossil corals fix the geological age of the rock. The temperature is uniformly 54 °F (12 °C), and the atmosphere is optically and chemically pure. There are gypsum rosettes and helictites.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).