The Lakewalk spans all the way from Canal Park to the Rose Garden. Both places are good spots to park and hop on the boardwalk. Be sure to stop and smell the roses and shop in Duluth Pack and other canal park stores too. Try to catch a sunrise or sunset along the lakeshore!
Drive over the lift bridge and keep going all the way to the end of MN Ave and you'll arrive at MN point. You can park and walk over the sand dunes to hang out at the beach. One of our favorite hikes in Duluth is down here. You can follow the paths to the end of the point through sand dunes and pine tree paths. If you don't want to drive all the way to the end of the point, you can park in the first beach lot about a half-mile over the lift bridge for some good beach time and views of the city on the hill.
If you want to hike or mountain bike or even camp these are great options! The SHT has a variety of length and terrain. Check out the link for maps from Duluth all the way up the North Shore.
Fitgers is known for their brewhouse, but there are also a bunch of cool + eclectic shops in their building. Check them out along the boardwalk! While you are there stop at the Portland Malt shop for a malt or ice cream along the boardwalk. Have a blueberry malt for Seth or a cookies and cream shake for me.