France is full of WWII military structures, viewable and open to the public. The Maginot Line is a good example of this, with numerous fortifications stretching from central Alsace to western Lorraine, that is France's border with Germany.
Construction started in 1930 and lasted for just less than ten years, built in principal to satisfy the French need to protect itself from Germany. The Maginot Line as we all know did not stop the Germans in 1940, but it did in part serve some of its purpose as the Germans where obligated to go around it.
Marckolsheim Maginot Line
Soufflenheim Maginot Line