The 12th-century archbishop's residence (Erkebispegården), commissioned around 1160 and Scandinavia's oldest secular building, is beside the cathedral. In its west wing, you'll find Norway's shimmering crown jewels and its museum. After visiting the well-displayed statues, gargoyles and carvings from the cathedral, drop to the lower level with a selection of the myriad artefacts revealed during the museum's late-1990s construction.
The palace also has an enjoyable 15-minute audiovisual program. If you're visiting Trondheim's cathedral, it's cheaper to buy the combination ticket, which covers admission to all three attractions (archbishop's palace, crown jewels and cathedral).