Boyen Fortress in Giżycko is one of the best-preserved Prussian fortresses in Europe. Built between 1844-1856 as a key defensive point of Eastern Prussia. Named after General Hermann von Boyen, Minister of War.
Hexagonal layout with 6 bastions covering 100 hectares — larger than many medieval cities. Stone walls, water moats, underground tunnels. Never captured in battle.
During WWII it served as headquarters of the Abwehr (German military intelligence) — Admiral Wilhelm Canaris worked here. The conference room is preserved in original condition.
Today it's a museum + open-air heritage park. Night events in the bunkers are organized regularly. Open 9:00-19:00. Ticket 20 PLN.