The cave first appears in the written record in 1541, already known and already being worked. It runs 610 metres through the dolomite of the Zechstein, a karst system dissolved out of stone laid down when a shallow sea evaporated across northern Europe. What made it valuable was what had died in it. Ice-age animals fell in, sheltered in it, or were dragged in by predators, and their bones accumulated in the sediment for tens of thousands of years. To a seventeenth-century digger, a fossil that large and that strange could only belong to one creature. Unicorn horn was among the most expensive substances in European medicine, and here was a hillside full of it, waiting for a shovel.

In 1686 Gottfried Wilhelm Leibniz came to see the cave for himself and wrote a report noting the local trade in unicorn artefacts. He was not merely a tourist. Otto von Guericke, the mayor of Magdeburg better known for proving the force of a vacuum with two hemispheres and a team of horses, had published an account of ancient bones dug from a Harz hill near Quedlinburg. Working from Guericke's description and from the material coming out of the cave, Leibniz produced a reconstruction of the unicorn's skeleton and included the drawing in his geological treatise Protogaea, which appeared after his death in 1749. The result is one of the great wrong pictures in the history of science: a hunched, hornless-bodied beast with a single enormous spike jutting from its skull, assembled with perfect logic from parts that never belonged together.

The correction came in 1872, when Rudolf Virchow excavated in the cave and identified the bones for what they were. No unicorns. Mammoths, cave bears, and a menagerie of other extinct and vanished animals. Over the years more than 70 species have been recognised in the deposits, including some 60 mammals, among them the cave lion and the wolf. Leibniz's skeleton turned out to be a cave bear and a mammoth pressed into service as a single creature, with a tusk for a horn. It is easy to laugh at, and harder to do better. Before comparative anatomy had matured, a pile of unfamiliar bones was a genuinely open question, and Leibniz answered it with the best framework available to him.

Then, in 2019, excavation at the cave's former natural entrance turned up something the seventeenth century would have found far stranger than a unicorn. A toe bone from a giant deer, boiled to soften it and then carved with three stacked chevrons and four short parallel lines, dated to roughly 51,000 years ago. That places it firmly in the Neanderthal world, before modern humans reached this part of Europe. The find was published in 2021 and is among the oldest known deliberate designs made in Europe. Giant deer were rare in the Harz and carried antlers spanning nearly four metres; the choice of bone looks like a choice, not a convenience. Somebody sat in this hillside and made a pattern for no practical reason at all.

An entrance gallery was cut in 1905 to let visitors in, and 270 of the cave's 610 metres are now open as the largest show cave in the West Harz. It serves as one of three information centres for the Harz - Brunswick Land - Eastphalia National Geopark and carries checkpoint 101 on the Harzer Wandernadel hiking network, so a steady traffic of walkers arrives with stamp books in hand. Local folklore supplies the ending the geology cannot. A pagan woman living near Scharzfeld was pursued by Frankish warriors under a monk in a black habit; a unicorn appeared, drove off the pursuers, and let her escape to join the witches on the Brocken. The monk, still running, fell into a deep hole. The hole, the story says, leads here.