🏰 Mjösjöfortet – Sweden’s Hidden Mountain Fortress 🇸🇪 Deep in the forests of northern Sweden lies Mjösjöfortet, part of the mighty Boden Fortress (Boden Fästning). Built between rocks, moss, and snow, it was once one of Sweden’s most important strongholds – constructed to defend the country from a possible invasion through Finland or Russia. The fort was built around 1900–1908 and became operational in 1910. It formed part of a defensive ring of five large forts surrounding the town of Boden.