1,000 years of limestone mines under Denmark.

In Mønsted Limestone Caves in Central Jutland there are more than 60 kilometres (about 37 miles) of underground paths. Some are as large as cathedrals and others are so narrow that a grown man cannot walk through them upright.
The caves are very old. When Denmark was becoming an increasingly Christian nation around the 11th century, limestone mining was a profitable industry because the stone was used in cathedrals.

These tunnels open up into various cave “rooms,” some of which contain entire underground lakes. Visitors to the Mønsted Kalkgruber museum can wander through the caves on their own or take a train ride tour throughout.

Inhabited by more than 18,000 bats.
The limestone caves are inhabited by more than 18,000 bats during winter. Mainly Daubenton’s bat (Myotis daubentonii) but also The Pond bat (Myotis dasycneme). During spring and summer the bats are active all over Jutland feeding on insects.

Visit the caves.
See opening hours and find more information about the caves at Monsted-Kalkgruber.dk

Sources: atlasobscura.com, monsted-kalkgruber.dk.