Several airlines have direct flights to Trondheim from Stockholm (Wideroe), Copenhagen (SAS Braatens) , Amsterdam (KLM) and London (Norwegian). In addition, there are good and frequent connections from Oslo and other Norwegian cities.
It is also possible to fly to Bergen, and catch the "Hurtigruten" coastal express to Trondheim and experience the fjords - or why not catch a train from Oslo to Bergen, and take a detour on the "Norway in a nutshell"-trip? A trip by train from Oslo to Trondheim, is a 7 hour journey through valleys and across montains in the heart of Norway.
The summer school attendees will get reduced rates at two hotels in Trondheim. Both are located in the city centre, within easy walking distance to the Summer School venue.