If you are up around the Duluth area I really like the Two Harbors (KTWM) airport. Nice long runway. And if you contact the airport guy in advance they will reserve a airport car for you
Landing at Duluth (KDLH a delta) is nice and the Cirrus are made there. I think there is some type of museum or tour. Nice FBO and not far from downtown.
If you are crossing Minnesota up in the northern half, my favorite airport is Brainerd (KBRD). Two nice long runways and restaurant right on the field which is rare for Minnesota.
Going west from Minnesota I really like the Sioux Falls airport (KFSD) and the Pierre (KPIR) airports of which only one will be on your way. Maverick FBO in Sioux Falls is awesome. To me, the Midwest starts to become the Outwest up north right at Pierre and hence their slogan at Mustang Aviation. Nice FBO. And the scenery with the Missouri and the large dam and lake is awesome. Plus, departing Pierre leaves about 50min to Rapid City. Which is perfect to get on with Ellsworth Approach and have them Vector to Mt.Rushmore and Crazy Horse. To me, from the air Crazy horse is more impressive. You can flight directly across from it. We just circled around it and this tiny mountain to the east several times. Very cool.
The FBO at Rapid City (KRAP) is very nice. More importantly, its a regional commuter airport so there is a standard rental car building literally like 2 blocks walk from the FBO. The downside to KRAP is that it is a long ways from the downtown. If you get a car at KRAP and want to double back on I-90 to the east about an hour or so you can see badlands and its really cool.
The other way to see the badlands in that area is to land at Wall (6V4). Plus this is the "Wall Drugstore" that is a staple of that area. The airport is pretty close to town. Just not sure if they have a car. But you are literally just a few miles from the best entrance to the Badlands, awesome pictures, etc.
Also by Wall are (3) Minute Man missile silo museum sites. One is a view of a silo. One I think is a tour of a launch facility. And One is a actual Museum which is very nice. As the land slowly passed you by in the area (to the north of the I90) you might start spotting all the old decommission silo sites.
Personally, I think one of the best places to land is Spearfish (KSPF).
We were just out there (driving trip). If there is any way you can see Devils Tower from the air I bet it is awesome. But find a way, even if it means driving a car from Spearfish, to go and see it directly.
Custer (KCUT) is also a great airport in a great location!
We did the Jewel Caves and it was awesome. I think the Wind Caves are also awesome but they are different. We did not care for the Mammoth part of the trip.
If you do the Needles Highway drive from south towards Mt.Rushmore, you will drive through a couple of carved out short tunnels. IIRC, both directly face "The Faces" which makes for a great camera shot or video clip.
Keystone is at the base of Mt.Rushmore and has a few western themed restaurants.
The best light is on Mt.Rushmore in the morning.
The Mt.Rushmore guided talk down in the artists/creators building was really cool.
I've driven it more than flown it. Coming from the east as you get to KRAP you will start to see some pretty high DA's as compared to the flatlands...maybe good practice for going farther west!
If you decide to cut the northern part out and are going for time across the Twin Cities area, there is a great restuaurant on the field at Eau Claire (KEAU) and a even better one right on the field at downtown St.Paul (KSTP) call Holman's Table.
The early evening flying out here is awesome...especially if your plane isn't broke