Much of what Albert Speer had planned never got realized. This is one of the two rallying grounds that were actually used.
You probably have seen Zeppelin Field in Leni Riefenstahl’s “Triumph of the Will”. If not, you can do so on YouTube.
Why should I see a propaganda movie, you ask? Well, for instance because it’s an incredibly effective propaganda movie as such, and it is always useful to learn about how manipulation works. Leni Riefenstahl definitely knew how to present a crowd.