Wizernes
Just outside Wizernes in northern France, the Germans began in 1943 to build a missile base for launching V2 missiles. The Base was called Bauvorhaben 21. The V2 was a further development of the V1 bomb/rocket and its purpose (and V1) was to spread terror and destruction in London and southern England. The base was built inside a mountain and consisted of a covered tunnel system and was the largest base of its kind built by the Germans. But the British had through intelligence recieved information about the base and it was bombed repeatedly. Therefore it was never completed and never became operational. The base was occupied by the allies in September 1944.
Current status: Partly preserved/demolished with museum (2017).
Location: 50°42'18"N 2°14'37"E
Get there: Car.
Follow up in books: Irons, Roy: Hitler’s Terror Weapons: The Price of Vengeance (2013).
It might be worth thinking about the Germans getting their rocket bases in order and operational. Could that have had an impact of the war? We will never know the answer of that of course, but it’s worth a thought. But it’s clear that the allies took all this very seriously and more or less bombed the German rocket development back to the stone age. The museum itself is worth a visit, especially the models over various bases that the Germans built/planned to build. It also gives an idea of how huge and how complicated a base like this was. In addition to the Second World War, the museum also covers space development from 1945 until our days.