Back in 2010 I was learning German and visited Berlin for the first time with another friend whose German was as bad as mine. We downloaded this random app (in German) telling us about Berlin tourist attractions, and upon reading it we "understood" that Tempelhof was a tourist attraction and "frozen in time" and we should visit it.
We walked into the building looking for tickets for some sort of exposition, but there was no one inside - not even security. We genuinely believed it was a place open for guests, so we just walked straight in. We toured inside of the airport alone for about 40 minutes, through the hangars and corridors and up and down a couple of rooms and staircases. The most curious room we found was some sort of poorly lit restaurant that had tableware with eagles drawn on it, and a cute old bar which I suspect is what one would find in Germany during the Cold War.
Most doors were unlocked one way, but would lock such that you couldn't walk back where you came from, and thus kept pushing us to go further and further in. The place is huge though, and we didn't see many of the things shown in the pictures in the posted link, not even the main hall.
Finally a guard found us and politely escorted us out of the building. We figured the airport was closed because it was Sunday, and it actually took me a couple of years and other visits to Berlin to realize the building wasn't open for the public.
One of my greatest experiences of being lost in translation.