Carlsbad Caverns National Park

So far some 22mi/35km of passages have been explored. A 3mi/5km tour takes visitors through the main cave and a series of spectacular chambers containing stalactites and stalagmites.The caves are home to vast swarms of bats whose evening antics have long attracted fascinated audiences. Up until the 1920s the abundant supplies of bat guano in the outer reaches of the caves provided a much valued source of fertilizer.Origin of the cavesThe cave system has been created over many millions of years, and the process is still continuing. Some 200-250 million years ago calcareous sediments were deposited by a warm sea, and thereafter upthrusts and subsidences of the earth's crust in this part of the world, advances and retreats of the sea and varying climatic conditions brought about chemical disintegration processes which were particularly active during the rise in the level of the land which took place some 40-20 million years ago. Groundwater and rainwater seeped into the limestone through fissures and crevices, creating cavities which grew steadily larger. In course of time the water filtering through the rock, with its high lime content, created the marvelous stalactites and stalagmites and the waterfall-like limestone terraces to be seen today.There are different types of tours, starting from the Visitor Center.