Trondheim is a nice city. Very walkable city center, with bus, train, near by. The airport is way out of town to the NorthEast but the train stops there and can get you into town. Train, If I recall correctly, also stops in Melhus. Have a great trip.
If you have time before you go, contact the local library they may be able to help. If you don't have time before you leave, contact them when you arrive in Trondheim. They probably have a good local contact, a book, map or may be related!