Anywhere along the lake is scenic but I've had alot of fun just in Duluth. This campground has full hookups available as well as Wi-Fi...
Campsites | Indian Point Campground, Duluth Minnesota
It's bordered by the St. Louis River, has paths and some boat rentals. Been there, small and nice. I don't know how busy they are or how late in the season they are open.
If your exploring Duluth, a few high points for me are:
The Karpeles Document Museuem
Corps of Engineers Center at Canal Park
Railroad Museum (lots of steam locomotives)
Road of Seven Bridges
The Duluth Grill (nice restaurant)
The Congdon Mansion (staff won't talk about the murder, the full tour goes to the top floor where they show some of the structure, kinda expensive but well worth it)
In Superior, Wisc.:
The Whaleback freighter Meteor
Bong Travel Center/Reststop (pay to tour the downstairs exhibits, well worth it)
Duluth has a decent park system and a nice lakewalk.
For day trips outside of Duluth there are some stops I can recommend:
The Soudan Mine
Hull-Rust-Mahoning Mine in Hibbing (a very large hole)
The Palisades Scenic Overlook (tight drive!)
In Washburn Wisc. there is used bookseller. Many titles are old and eclectic or odd. If you like books you'll find something.