Among your first stops should be Trondheim Tourist Information Centre. Here, you'll be able to orient yourself and get some great ideas before you start exploring.
This Trondheim City Centre tourist information center is an interesting place to begin your day of sightseeing. There's plenty to discover nearby, like Nidaros Cathedral, Sverresborg Trondelag Folk Museum, and Archbishop's Palace. Wander around at your leisure at Trondheim Tourist Information Centre before heading to these other fine sights.