That little corner where the 3 states meet does have some weird geography. President Grants home/museum is in that area iirc. Driving across 90 can get you within spitting distance of several Presidential homes, actually, if that's interesting to you.
In Sioux Falls, SD the zoo has a whole building for a stuffed animal collection that was donated by one of the most prolific big game hunters in the country from a hundred years ago. Elephants, lions, etc... stuff that childhood me found fascinating.
If you are into musical instruments or their history then you want to swing through Vermillion, SD, my home town, and visit the museum there. It used to be called the Shrine to Music museum, but I think they changed it recently. The instrument collection is so big that they are routinely loaning out Strats and such to the Smithsonian or other museums to build exhibits around.
RossD said:
Check out the driftless zone. Its where glaciers never wiped the geography off the landscape.
https://driftlesswisconsin.com/
Its located by the Mississippi River kind of by where Iowa, Minnesota and Wisconsin meet. Fun roads good views. Little tourist spots sprinkled around.
The area around La Crosse, WI and Winona, MN is pretty picturesque. If you want to do a slight detour off I-90, drive up the River Road along the Mississippi to Red Wing, MN - it's a neat little town with a nice hotel (the St. James), the Sheldon auditorium that often features good musical and theatrical performances, and is also the home of Red Wing shoes (they have the world's largest boot on display in their museum.) It's not much further to get to the Minneapolis-St. Paul metro area, and there are all kinds of things to see and do here; something you may be interested in is the local transportation museum offers rides in restored streetcars, as well as on a restored excursion boat in Lake Minnetonka.)
Back down along I-90, a stop at the Mayo Clinic in Rochester, MN would be interesting. They offer free guided tours of the public areas, or you can check it out on your own. The complex itself is pretty cool, and they have lots of art and historical items on display including a large collection of Dale Chihuly blown glass.
The ball of twine is in Darwin, MN, about 60 miles west of Minneapolis, but I wouldn't go all the way there just for that. 
You can head north from the Missouri River, go through some pretty areas of an Indian reservation on 2 lanes and come out at the state capital, Pierre. Pronounced "Peer." Then head west over more 2 lane and come out at Wall Drug. We do that occasionally. There's actually a good TexMex restaurant in Pierre, next to the Super 8 Motel. Here's a pic of me at that Super 8 on one of our trips:
The Badlands and Custer State Park are worth the small detour off of I90
Robbie
UltimaDork
7/5/19 10:55 a.m.
If you're stopping here in Chicago we'll put together a Chicagoland meetup for dinner or you guys can stay at my place for the night.
Robbie said:
If you're stopping here in Chicago we'll put together a Chicagoland meetup for dinner or you guys can stay at my place for the night.
Yes. This. A million times this.
No one mentioned Niagara Falls. Before you even get out of NYS.
TJL
Reader
7/6/19 11:54 a.m.
Im more familiar with the south dakota parts, but certainly sioux falls. It has some great Vietnamese food(Lams and Phnom Penh) and the falls park is nice.
Of course the badlands, rushmore is there if you have never seen it. Or venture a bit further to devils tower in wyoming. On a fanily vacation many years ago we hit the corn palace and also in mitchel SD there was a mustang/shelby museum. Just a collection of some very rare nice fords. Guy had a real shelby cobra. Funny thing was a guy that was touring it with my dad, bro and me took his camera out to snap a pic. Carefully laid his cloth camera bag on soft top cover for the cobra and the owner/tour guide about lost his crap, BUT thats funny because the owner put his poodle dog IN the cobra to chill.
In south dakota or really most of your travel there will be these amazing little farm towns that havent been really corrupted with big city crap. Usually a neat very “historic” downtown area with a local bakery and some cool shops/sights. Real mayberry places.
In reply to Wally :
US 20 is an east west option.
Slower but no tolls. Lots of neat small towns.
If you want some cheese and can't wait until you get to Wisconsin, you might enjoy Cheesehaven in Sandusky Ohio. They have a good selection of cheese, a lot of absurdly named hot sauces, novelty items with cuss words on 'em, and of course some smoked meats to go with the cheese.
NOHOME
MegaDork
7/6/19 3:24 p.m.
Not much between Sioux Falls and Rapid City.
The Air force Museum in Rapid is Free and awesome
The Badlands are awesome
The Minuteman Museum, a testament to the cold war is awesome
Rushmore is so so, Crazy Horse is awesome
Done the I90 drive across SD 20 or 30 times, the most memorable state crossing was when I went south and took 44 across the state. I was 30 years old, had a brand new Miata and more $$$ than I knew what to do with so I could pay fines or bail, so I did the trip pedal to the metal and it was AWESOME. Bonus is your roll into Rapid through interior and the Badlands.
Pete
In reply to stuart in mn :
The Mayo Clinic on the way is good to know, we’ve enjoyed seeing Chihuly exhibits before. Hopefully we won’t need a hospital this trip but it’s good to know where they are. 60 miles for the ball of twine isn’t a dealbreaker just because I know it would infuriate my mother in law.
In reply to Robbie :
When I have a better idea when we will be there I will be sure to let you know.
In reply to iceracer :
I’ve done Niagra falls before, since we’re trying to go so far west we probably won’t stop much in NY
On your way through Erie, PA you could stop on Presque Isle for a loop around the state park (30min). There are nice fresh water beaches, light houses, and some occasional wild life. If you go through near dusk find your way over to the lake for an awesome sun set.
As for food I highly recomend Lucky Louie's beer and weiners. Order up a Happy Ending, Italian Job, or American A.F. made with local Smiths hot dogs loaded to the gills with toppings. Great beer selection as well. A good runner up would be Federal Hill BBQ.
In reply to slowbird :
I think legally as a tourist you can only buy cheese in Wisconsin.
When I think Sandusky I think of these thin kitchen storage cabinets that we would sell at Kmart in 1981 not cheese. They always arrived at our store all dented up.
In reply to Datsun310Guy :
I mean, sure, yeah, Wisconsin is probably the best place to get cheese, but...I've bought cheese in Wisconsin, Missouri, and two different places in Ohio. It's all been pretty good.
