You can spend hours wandering around the city's old port area at the mouth of the River Nidelv. Colorful old wooden warehouses, many of them converted to classy boutiques and high-end homes, are built on piles above the water.
The best view of these buildings is from the water, and a wide variety of harbor tour options are available. Be sure to visit the Trondheim Maritime Museum with its model ships and displays illustrating the city's deep-rooted connection to the sea.