Norra Djurgården's tank barrier in Liljanskogen.

In Liljans forest. It was part of Stockholm's inner H-line (main line of defense) The line through Norra Djurgården was built during World War II and contained tank barriers, foxholes, shelters and places in a line from Brunnsviken in the west, past Laduviken to Husarviken in the east, a distance of just under three kilometers. Wikipedia.