My office is 5419 in the Hillman Center for Future Technologies ("Hillman"), which is part of the Gates Hillman Complex (GHC). If you need to ask someone for directions, most people will know where Gates is; Hillman is less well-known.
The Language Technologies Institute has a reasonably good visitors page that has information about finding CMU, hotels, parking, campus maps, etc. It is a good place to start.