Visit the Kristansten Fortress! It was built the year after the city fire,in 1682.
The only time the fortress has been in battle,was in 1718. King Karl XII of Sweden attacked Norway,and his army tried to seize Trondheim. Because of the fortress they failed. The soldiers retreated back to Sweden,and on the way over the mountains in January 1719 around 2200 Swedish soldiers froze to death. Some 5-600 died later of related injuries.
Favorite thing: We went here and had a great view, I could even see the tower where we had dinner. It's quite interesting but the fortress is undergoing some restauration so there are fences and stuff disturbign the nice images.
Lets follow this street to the top of the little hill.
At the top we find an old fortress and we have a nice view over the town(I Hope so)