One of the more charming things about the first season of Buffy the Vampire Slayer is that Sunnydale High School consists entirely of a library and a single corridor. They clearly had no more sets, so everything happens in that corridor. (The library is a place of comfort for the four main characters, and doesn't really count). As the budget got a little bigger, the school got more rooms. Then it was eaten by the principal after he had turned into a giant snake in the season 3 finale, and the show was never the same again.
How I miss it.
The one with the corridors is great. Strange that it doesn't have the ones from 2001 though.