Fort Heldsberg, Military fortress museum in St. Margrethen, Switzerland.

Fort Heldsberg is a military fortress near St. Margrethen that displays equipment, documents, and defense installations from Swiss military operations. The structure contains multiple restored rooms where artifacts and information about the fortification's use are organized and presented.

Built between 1938 and 1941 after Austria's annexation by Germany, Fort Heldsberg guarded the Rhine crossing near St. Margrethen. Its four 75 mm guns, with a range of 10.5 km, could shell Bregenz and Lindau. German planners judged an attack at Rheineck (Heldsberg) unpromising. The fort remained in service until decommissioned in 1992.

The fort functions as a place where visitors can observe how Swiss defense strategies shaped daily routines inside the fortification. Personal items, uniforms, and equipment on display reveal the lives of those who worked within these walls.

The fort is entered from the rear of the Heldsberg slope, close to the underground utility plant and barracks, and the tour follows 1,000 m of tunnels between the gun blocks and observation posts. Bring a jacket, since the underground passages stay cool, and allow time for stairs and uneven ground.

The facility still displays original artillery positions and defense installations from its operational period. These preserved installations allow visitors to directly understand how a border fortress of that era was physically arranged and functioned.