I am in Trondheim for work in Sept. I don't have a car. Where do you recommend going for a day hiking or kayaking?
Also any special restaurants or nightspots?
I was only in Trondheim for a few hours, but seeing that you haven't received any other replies yet...
The old center seemed to have the usual selection of restaurants. I ate at some place that specialized in interesting Norwegian takes on the hamburger (I can't remember the name). Might want to check it out if nothing else sparks your interest. I saw that one restaurant actually had ludafisk on the menu, but I didn't try it.
The Way of St. Olaf ends in Trondheim, but I have no experience hiking this trail. Parts of the trail go through some amazing back-country as you approach the Swedish border and further into Sweden, but without a car, these sections of the trail are too remote for a day hike.
For day hiking you could hike right into the woods around the city. Here's a good page in english from a local university: https://www.ntnu.edu/livingintrh/about-trondheim/bymarka It focuses on where you can find waffles and coffee or cocoa in the mountains, which is critical to your Norwegian day hike.