Måndalsfortet was a defensive fortification located on Måndalshöjden, next to Måndalsstigen in Tyresö. The fort was part of the Southern Front, which was constructed shortly before and during the First World War.
The Southern Front and the Northern Front, also known as the "Korvlinjen" (Sausage Line) were key components of Stockholm’s fixed defenses. One of the best-preserved installations is Måndalsfortet; construction began in 1903, and the fort remained part of the defense system until 1952.
I can really recommend coming here and it's not far from the city (Stockholm).
