No real WW2 boats I'm afraid.
Only seen the "Das Boot" prop in Bavaria Studios Munich which is a 1:1 scale interior model that cannot be opened and can only be accessed through the aft torpedo room, the bow torpedo room and an access halfway through. Therefore the experience to a real sub is similar. Also had a look into U-1 in the "Deutsches Museum" also in Munich. It's been cut open, so you can't go inside but get a good impression on how damned crowded it was.
The only real boats I was inside were a Typ 206A class German uboat (U-9) in Speyer, Germany, which is much smaller than a Typ VII C.
http://www.mx-5-roadster.de/Speyer/images/a_U-9.jpg
http://www.mx-5-roadster.de/Speyer/i..._zentrale2.jpg
http://www.mx-5-roadster.de/Speyer/i..._zentrale1.jpg
They also have a German Mini uboat there which is hardly larger, than a torpedo.
http://www.mx-5-roadster.de/Speyer/images/a_04.jpg
And then there was a visit to a Russian Foxtrott in Greenwich, UK.
http://www.mx-5-roadster.de/London/L_sub.jpg