A bove ground, you probably won’t notice anything. If you don’t know, all you’ll see is beautiful forest and grassland, part of the protected Natura 2000 landscape of mid-Jutland, spreading out around you. As you head past the old lime plant, held in place by massive grey chimneys, note the gentle rustle of stray wheat on the roadside, the smell of pine; the frantic flapping of a leathery wing, perhaps, as you inevitably make your way towards the dark tunnel ahead. Let the cool air greet you as you step inside. There’s a whole other world just underground, just waiting for you.

The world’s largest limestone mine is well-hidden, yes, but it’s right there and yours to discover, no matter who you are. It’s always a steady eight degrees down there, the humidity a demanding 98 per cent. The place is enormous. The people who work at Mønsted Kalkgruber know of roughly 60 kilometres of tunnels and caves snaking out across the area, and there might be many more. Some places are cordoned off for safety, but most of the underground walls, rivers and tunnels are free to climb and explore. Those less able or willing to run wild are just as welcome; the first parts of the tunnel system have been smoothed out, making space for everyone including wheelchair users to roam around underground. The first two kilometres are illuminated.

Mønsted Kalkgruber is human-made. It all started a millennium ago, when Danes needed mortar for the construction of the country’s first stone buildings. People have been carving out pieces of Mønsted since at least 1060. “It was the normal peasants of the area who made an extra penny digging out the lime,” says tour guide Søren Frandsen. “That’s how it continued for centuries. The chalk was brought to a building site and mixed with sand and water, creating a top-notch paste not unlike feta; the same mortar holding together the churches, cathedrals and other ancient buildings left to us today. At first, the Mønsted locals carved out simple holes in the ground, but as demand grew, they started tunnelling, constructing mines. Some people chipped at the walls; others, often women, carried out the big pieces.”

Newer tunnels could become several metres high. Over time, lesser limestone pieces would be trod into the floor of the tunnels, raising the floor year by year until the carriers had to hunch over to move their haul through them. “There were quite a few similar, small quarries scattered around Denmark through the Middle Ages, nothing very special at all about Mønsted,” Frandsen says. “Then all that changed.”

Mønsted Kalkgruber

Chalk it up to luck

Industrialisation hit Denmark in the 19th century. Going with the spirit of the time, the King himself visited Mønsted and decided processes could be improved. The carriers were replaced by little ponies for a while, and then, for some reason, in the 1870s, the Mønsted limestone mine was heavily industrialised, the only one in Denmark to be so. No one quite knows why the area’s farmers decided to sell or why the investor decided to buy Mønsted specifically, but the mine was rapidly expanded and tramways were put in, replaced by a railway in the 1920s. During its heyday, Mønsted limestone was all the rage, and chalk was used in everything from roads to agriculture. By the 1970s, demand for Mønsted limestone had slowed to a trickle. Only two men worked down the world’s largest limestone mine, and it lay largely forgotten.

Mønsted Kalkgruber

“Then, in the 1980s, someone came along and bought it,” says Louise Nielsen, Mønsted’s sales and marketing manager. “Rather intriguingly, it was the famous violinist Anker Buch, who had the ingenious idea to hold concerts down the old caverns. Soon, other musicians joined him in what became a chilly but rather magical experience.”

Today, during the summer season from May to August, a train once again transports passengers down the mine. Arla has moved into some of the caves, making a special cheese that thrives in the chilly, steady conditions of the cave. Visitors are greeted by an underground cinema in which the story of the mine is sketched out. Then, they are free to explore. “We purposefully don’t put up too much information or distraction down the mine itself,” Nielsen notes. “We’ve got a museum up here, and visitors can explore the old lime plant, too, but once you’re down the tunnels and caves, nothing should take away from the sheer awe of being there.”

“The place is unique,” Frandsen says. “Nothing really compares to it.” At Mønsted Kalkgruber, nature has joined up with human endeavour to create a mysterious underworld just beneath our feet. “It’s a beautiful, fascinating, unsettling place,” Nielsen concludes. “It’s truly magical.” When evening falls in winter, look out. That’s when the mine’s 18,000 bats come out to play.

Mønsted Kalkgruber is open from 4 April until 31 October. The mine train runs between 15 May and 15 August.

Admission is free for AarhusCard holders. Tickets are half price for those with season tickets to the Energy Museum or Verdenskortet, and discounts are available for groups.

Private tours can be booked in advance in English, Danish or German. For more information, get in touch with Mønsted Kalkgruber directly.

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