Trondheim has an efficient public transportation system with buses and trams that connect most areas of the city. A 24-hour ticket costs 130 NOK and allows unlimited travel. Taxis are also available, but can be expensive.
If you want to fully explore Trondheim and its surroundings, consider adding an extra day or two. If you are short on time, prioritize the attractions based on your interests and the estimated time spent at each place.