If you can't find a direct flight we suggest to go via Copenhagen or Amsterdam and then directly to Trondheim. If you arrive in Oslo (or any other Norwegian city) you need to pass the customs and then pass a new security check, and that can take some extra time. When leaving Trondheim, traveling through Oslo does not take extra time because you do not have to pass the security check. If you enter Norway by Oslo we recommend that you only travel with hand luggage.
Bus departures from the airport are synchronised with arriving planes. Even if your plane is delayed, you are guaranteed that there will be a bus leaving for the city, no matter how late your plane arrives.
The ticket costs 130 kroner (NOK) per person, and you can pay with a credit card if you have not been able to get Norwegian cash. The journey time is about 30-40 minutes.
There are two airport bus companies, the one called "Værnesekspressen" has departures that go to/leave from a stop close to NTNU/SINTEF twice an hour (see stop "Prestegårdsjordet" in this map:http://kart.gulesider.no/m/nUwse - when going to the airport, remember to cross the road; the bus will be heading up the hill, to your left as you walk from SINTEF). The bus leaves for the airport 14 minutes and 44 minutes past the hour, and arrives at the airport approximately 50 minutes later. See http://vaernesekspressen.no/index.php/vaernes_eng/vaernes/nyheter for more info.
If leaving directly from NTNU/SINTEF it may be most convenient to use the local train which leaves right outside the SINTEF offices. At peak hours the train leaves twice an hour; check https://www.nsb.no/?lang=en_US for updated time tables. The ticket costs NOK 75 and can be bought on the train, also using credit cards.
Trondheim has a small airport. If you arrive 1 hour before your flight you have enough time, also for international departures. So, if taking the airport bus from NTNU/SINTEF you should board the bus about two hours before your departure.
We also recommend Britannia Hotel (http://britannia.no/?lang=en). If you stay at Britannia you get FREE access to the best SPA in town.
A budget alternative is Pilegrimsgården: http://pilegrimsgarden.pilegrimsleden.no/en#
You can find a number of other hotels in Trondheim here: http://www.trondheim.no/accommodation/