On foot, Trondheim
Some of the intersections can be crossed diagonally, but be carefull which intersections you do that. It's not allowed in all intersections. Some intersections will only allow you to pass one way at the time, while cars drive in parallell. See if the pedestrian light is green in both ways before doing a diagonal crossing.
As I mentioned before, we arrived in Trondheim by train, spent some 6 hours there and left by train again. During our stay in Trondheim we walked all the time, but we also noticed buses, taxis, the bicycle lift and other means of transportation. Oh, and yes, Trondheim does have an airport as well! For some good information on the possibilites, have a look at the Trondheim transportation possibilities!