Lots of good hiking spots around Duluth. Ely's Peak, Hawk's Ridge, Hartly Nature Center have nice trails. Enger Tower is a nice lookout spot to get a high up view of the city, and they've got some hiking trails around it.
Duluth has lots of microbreweries around town. some of our favorites are in the Lincoln Park craft district: Ursa Minor Bent Paddle Duluth Cider Wild State Cider Two Harbors also has Castle Danger.
As stated above it could potentially be very busy down in Canal Park on Saturday due to the Inline Marathon finishing down there. Lots of little shops, and restaurants to go to. Boardwalk to walk along by the canal and farther out. They have electric scooters, and group peddle bikes you can rent as well. You can also check out the ship schedule here to see if any ships are coming through https://canalpark.com/duluth-ship-schedule/.
Beautiful rose garden to walk through and a cool outdoor theater down by the lake. Haven't been down there recently so not sure how much is in bloom, but still pretty to go to. It's also along the boardwalk so you can venture down that for a bit as well. There's also the Portland Malt Shop by the Fitgers building that has amazing malts!
They have an adventure park at Spirit Mountain which has a fun Alpine Coaster (more rollercoaster like, not the concrete track type), a zipline with bucket seats to sit in, a jumping pillow, a 9 hole mini golf, and disc golf course.
Located in Superior on Barkers Island.
Cool train museum, and train rides available as well.