Røros, a 2 hour train ride away, is well worth a day trip. An old mining town which has been added to the World Heritage list. Beautiful old mining buildings, and you can take a trip down the mine. Beware this is a 13km ride away, taxis charge a fair bit for the journey.
I suggest a trip to Monkholmen, it's only a 15 minute ferry ride away and gives you a great view back towards the city. The guided tour of the island is good fun, the place oozes history.
Trondheim has the clean, fresh atmosphere of a small city, but the variety and possibilities of a big city. Friendly, but hardy people. Most younger people speak good English.
Trondheim, located in about the middle of Norway, is a city of culture, education and history. It's home to approximately 170,000 Norwegians and is over a thousand years old. Trondheim also boasts many sights and interesting things to do for a traveler.
Trondheim is accessible by most means of transport: there is an airport (Trondheim Airport) which has regular scheduled flights to and from many locations. Trondheim can also be reached by trains, buses, and of course your own car. The buses are the most cost-efficient but not most time-efficient option. There is also a steamer running between Bergen and Trondheim which is a very nice trip.
Once you're checked in to your Trondheim hostel, getting around the city is easy thanks to a comprehensive bus network. You can also walk, but the main city area is a bit spread out.
Hostels in Trondheim are of high standard, but like most parts of Norway, a bit on the pricey side. Expect to pay 25 - 30 euros for a dorm bed and a bit more for double / twin rooms.
There are plenty of things to do and see when you visit a Trondheim hostel. The shores of the Nivelda river are a beautiful place to spend the day . For those who are into culture, there are countless options: the largest church in Northern Europe (called Nidarosdomen), the Archbishop's Palace, museums, galleries, and so on. If you visit in the summer, there are many places where you can have a nice swim, and in the winter the skiing in Trondheim is great.