St. Margrethen, Italy
Fort Heldsberg was built 1938–1940 near St. Margrethen in Switzerland, overlooking the Rhine, which forms the Swiss-Austrian border at that location, just south of Lake Constance. The fort was part of the Swiss Border Line defenses, built between 1938 and 1941. Since 1993 it is a museum.
Listen to the audio guide for Fort Heldsberg Free on WIP — starts by itself when you arrive, even with the screen off