From infamous haunted hotels to stories of spooky hiking trails and cannibalism, Colorado has no shortage of blood-curdling tales and landmarks.

One such legend of a slightly tamer degree is that of “tommyknockers” – notoriously mischievous goblin-like creatures known for playing tricks in Colorado mines.

The mines built in Colorado during the gold and silver rushes of the 1800s brought with them the urban legend of the ‘tommyknockers,’ according to reporting from KDVR. According to the UK’s National Coal Mining Museum, tommyknockers inhabit a variety of mines around the world, with the legends of the tommyknockers brought to the U.S. by migrant miners.

The National Coal Mining Museum describes the creatures as about two feet tall with white whiskers. They are said to wear traditional mining clothes.

The tommyknockers were known for pulling pranks like hiding miners’ tools, taking bites out of someone’s snack, and extinguishing lights.

The folk tale reportedly originates from the British Isles in the late-1800s. It was a popular myth among Cornish immigrants, according to History Colorado. They believed that the creatures living in the mines caused the knocking noises, but the reason as to why is somewhat of a mystery.

One theory is that the creatures are spirits of former miners looking after and protecting miners currently working. Some accounts even say that the Tommyknockers would give miners information about when they were about to hit a “lucrative vein.” KDVR says the story developed into superstition as mining became more industrialized and safety declined.

While tommyknockers aren’t the most well-known creature lurking around Colorado, they certainly have a place in the state’s local lore. The gnome-like creatures are still talked about in old west mining towns such as Idaho Springs.

In fact, Idaho Springs’ Tommyknocker Brewery & Pub is named after the devious beings.

Want to check out a bit of mining culture for yourself? Head to Idaho Springs for the Argo Gold Mine Tour.