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Photo: Ringve, CC BY-SA 3.0 via Wikimedia Commons
Norwegian national museum of music which also includes the Ringve botanical gardens of Trondheim. The garden grounds themselves are free to visit.
Ringve Museum is Norway's national museum for music and musical instruments, with collections from all over the world.
© OpenStreetMap contributors
Tyholttårnet
TV-tower with a rotating top restaurant: Egon Tårnet (see eat section).
Kristiansten festning
A fortress on a hill overlooking the centre. Have a walk in the area for views of Trondheim one can take the bus 25 to Ankersgata, or rent a bike and use the bike lift at Trampe.
The city library is built upon the ruins of a medieval church and some archaeological objects are on display. The building, which was built as the original city hall in the 19th century, is a remnant of the past. Also, being a library you can also borrow and read books, and it's the site of various events.
Trondheim Science Center
A center for popularizing science, has lots of exhibits, of which many are interactive. Also has a gift store. It is home to one of Norway's largest planetariums which was opened in 2017.