What is the most impressive spot in Berlin according to the woman?

M: Good morning Diane, fancy meeting you here. How is everything going these days?
W: Fine. You know, Alex, I just came back from Berlin.
M: Really? How did you like it?
W: The most memorable was the Berlin Olympic Stadium. Maybe it’s because I’m just a big sports fan.
M: Oh, tell me about it. You know, I have been thinking about going there on holidays in October.
W: Well, for the architectural design, it’s very complex but very beautiful, and it’s considered one of the best sports complexes built this century.
M: When was it open to the public?
W: It was first opened for the 1936 Olympic Games, the day of the marathon, a test of stamina over 42 km and the mass gymnastic displays outside the stadium were a breathtaking sight.
M: Don’t you wish you were there?
W: Definitely. But it’s sad when Hitler came in ruling, it got closed down. But now it’s just a beautiful, dimensional structure.
M: I see. Are there any other nice places you can recommend?
W: Oh, quite a lot. I will send you my itinerary tonight so you will know where I have been.
M: Thank you!