The map you're thinking of is called Library. It has three floors: a basement with mostly grey concrete walls, a middle floor with lots of glass partitions adn secret passages, and a top level mostly made up of walkways overlooking the middle floor.
In the N64 game, it was playable as a single map, but was also divided into two smaller maps:
- Basement, which consists of only the bottom floor
- Stack, which consists of the top two floors.