I toured the Pentagon as a high school student in 19XX.

The interior of the building is not all that interesting, in my memory. Lots and lots of hallways. We were told not to look through any open doors as we walked down the hallways. Somebody gave us a fairly cursory explanation of what they do at the Pentagon. (Hint: Lots of paperwork)

The interior courtyard was interesting if only for the fact that at the very center was a hot dog stand. I don't know if that's still true. But it's one of those things that sticks in your mind, especially as a teenager. Our tour guide said the hot dog stand was supposedly the deadliest place to stand during the Cold War. Obviously that joke became less funny after 9/11.

The tour was arranged by a teacher so I have no clue how it came about. It didn't seem like it was terribly unusual at the time, as the tour guide's presentation was done in the way that gave the impression she did it everyday.

Edited to add:

Here's an interesting article I found about the hot dog stand:
http://www.defenselink.mil/News/News...e.aspx?id=1049