Saint-Nazaire Submarine Base

Created during the Second World War, this huge bunker housed a German U-Boat base.
Saint-Nazaire, and you quickly realize this as you walk through the district, was heavily bombarded by the allies, but the base held out. Many operations were set up by the English to prevent the submarines from leaving the port, finally with success, but after the landing was created what was called the Pocket of Saint-Nazaire, making city the last city occupied by the coalition, after the fall of the Nazi regime.
This base is clearly worth the detour.

The Saint-Nazaire U-boat bunker is one of five German U-boat bases built on the French Atlantic coast during World War II. The 301-meter-long bunker was built in just 16 months in 1941/42 using almost half a million cubic meters of concrete. Several hundred men were stationed here until May 1945; offices, workshops, and a medical center were housed under the roof, which was up to 9.60 meters thick. It was built on the site of the former overseas port from which steamers departed for Central America.