The Atta Cave is located in Attendorn. This is one of the most visited caves in Germany and the main source of the town's revenue. It began to form 400 million years ago, when the region was on the sea floor. The cave was discovered in 1907, during the limestone extraction. The same year it was opened to tourists.
Unfortunately, photography is not allowed in the cave.
Getting there: By regional train from Essen and Düsseldorf (2 hours) or by train and bus from Cologne (3 hours).