Äventyrsgruvan Tuna-Hästberg (Tuna-Hästberg Adventure Mine)

Sweden has many mines that dot the landscape, many of which have been closed or abandoned. Some have been made accessible to the public, but often imposing strict rules and paths. This is not the case for the Tuna-Hästberg Adventure Mine, where almost nothing is off-limits.

The mine dates back to the 1600s, but most of its 12.5 miles (20 kilometers) of tunnels were dug in the late 19th and early 20th-centuries. The tunnels go down about 1,700 feet (520 meters) underground but are filled with water up to the 280 feet (85 meters). 

The mine is like a time capsule, with various items, sign boxes, and furniture still remaining since its closure in 1968. At higher levels, it was worth the effort to remove certain things, but the lower you go the more untouched it gets. However, the most impressive sight in the mine is the large pillared halls found throughout. These are a result of the various mining techniques of the day.

The mine is unique in its current operation, as it's run completely by a small group of passionate explorers who found the mine in their teens and snuck about it for years. Over time, they managed to buy the mine and started to make it more accessible for others, building staircases, digging tunnels, adding lights, and other amenities. 

Today, it's possible to explore the mine on foot or take a more adventurous route that includes zip lines and spelunking. Concerts are held in the mine's theatre room, and it's even possible to scuba dive down to the lower levels in the crystal clear, but icy cold, water.