You can choose any mode of transport which suits you. You could go by flight to this city, from anywhere in Europe. The airport is situated around 30 kilometers from the main city area.
There are a number of flights being operated in and out of Trondheim, by almost all the major airlines of Europe and other countries of the world. Alternately, you could also take very comfortable and frequent buses or by train. You could also try and move to this city by water. Hurtigruten is a coastal express that operates very comfortable boat cruises to this city. There is plethora of private taxis, which you could choose, in case you are very particular about your privacy.