Just for completeness…it’s the Mars Cheese Castle:
It’s just north of the IL/WI state line, on I-94 (and it’s right next to the highway).
Unfortunately, it’s not on the most direct route from Minneapolis to Chicago, unless you’re heading for Chicago’s northern suburbs (it’s usually a shorter trip to take I-90 through Rockford, rather than I-94 through Milwaukee).
Yeah, I don’t know why that is, but it’s true on both main routes into IL from WI (I-90 and I-94), though I think one of the ones on I-94 has either gone out of business or moved.
I drive the I-94 route a fair amount (I live in suburban Chicago, my family is in Green Bay). What always depressed me was making that drive on Christmas morning, and seeing a half-dozen cars parked in the adult bookstore parking lots. Very lonely men? Last-minute Christmas shopping? 
A cheese tour of Wisconsin - I like the sounds of that. I’ve heard so much about squeaky cheese curds - we’ll be sure to try those on the way.
Make sure to get some deep-fried cheese curds while you’re at it (can absolutely be found at a Culver’s restaurant, which you can find at pretty much any major interstate exit in Wisconsin). Like mozzerella sticks, but even better. 
If you end up coming through Madison, pm me for my phone number. It’d be nice to sit down for a meal or drink.
Will do. I think we will be driving right through Madison.
I’m assuming you’re taking 94, yeah?
There’s a BRILLIANT Mexican (not TexMex. Mexican.) restaurant in Melrose, just off the highway next to the Super 8. Large Latino culture there working in the bird factories and you wouldn’t believe what they can do with a chunk of beef. Don’t be put off by the dive-like atmosphere.
Melrose is about 7 miles from Freeport, which is widely believed to be the basis of Garrison Keillor’s Lake Wobegon.
St. John’s University is a bit further down the road. It’s home to one of the largest Benedictine monasteries in the world and has an incredibly interesting abbey built in a modernist/brutalist style. More importantly, however, they’ve spent millions in commissioning the St. John’s Bible, and the “Wisdom Books” will be on display through December (the rest of it is traveling right now). The bible has been news here for yeeeeeeeeeears so I got a little tired of it and was rather blase when I bought the tickets to see it at the Minneapolis Institute of Arts. Then I saw it. Fucking stunning. The beauty and craftsmanship completely and utterly blew me away - and I’m an athiest! I strongly encourage you to take the time to see it, if you’re able, but do check the website as the Hill Museum’s winter hours are weird.
St. Cloud (where I live) is another 45 minutes down the highway. The only attraction, as far as I’m concerned, are the Clemens and Munsinger gardens along the Mississippi but nothing’s going to be blooming this weekend - frankly, it’s getting to the point where I decide that nothing’s actually going to bloom until August. Anyhow, if you shoot me an email at rsandy at gmail dot com I’ll treat y’all to a meal at a Somali restaurant here in town.
The Charles A. Lindberg Boyhood Home and Museum is in Little Falls, about 45 minutes north of here. Not a must-see on the scale of, say, the Grand Canyon, but well worth a stop.
For the cheese factor, the World’s Largest Ball of Twine lives in Darwin, 30 minutes south of here. 
It sounded like you’d come through on the weekend. No fresh curds them. Some places only make them on certain days, because they gather milk from their suppliers to make a full batch so check by phone or web site before you drive out of your way. The center of Wisconsin along the interstate has very few cheese makers. Most of that is potato and cranberry growing country. Always ask when the curd was made, because shops will try to pass old curd off as fresh. There are a few plants that make terrible curd too, but that is very rare. I could suggest plants if you can say the route through Wisconsin. Stop in Culver’s when you drive trough Wisconsin. They have great food and be sure you have the frozen custard.
The cheese curds are 50% cheddar ones and 50% mozzarella ones.
It sounds like there’s an art to getting a proper cheese curd. So, how old is an old curd? Are we talking curds made within hours of buying them are the only proper ones?
They’re best within half a day of being made, and the next morning they are OK. Do not refrigerate them or leave them in the car window on a sunny day. The good ones are salty and moist. A day after they are made, much of the moisture is gone. You can microwave them in ten second intervals the next day and they are a little better.
It comes down to if it doesn’t squeak when you eat it, it’s getting old. Fresh curd is squeaky curd.
Older cheese curd is fine, it’s just not the same stuff we rave about. Once I got fresh string cheese from my favorite producer. It was only an hour old, and I could have ate 10 pounds in a sitting. You will want to eat pounds of fresh curd in a sitting. Buy more than you think you’ll eat. 
Oh, lord, we are already huge cheese-eaters. I’m scared of cheese curds now!
If you’re afraid you’re going to OD on cheese, Wisconsin may not be the best place for you.
I love cheese curds! I don’t know why you can’t seem to find them anywhere but WI. Cross the line, and voila! Readily available cheese curds! I’m sure they’d do well in Chicago, but nooooo, I’ve never seen curds there. (I’m hoping this is the point where someone jumps in to post where you can find them in Chicago.)
If you go to Culver’s, try the frozen custard. It is delicious.
If you are on 1-94 in WI, visit my favorite cheese place, Cady Cheese.
It’s about 25-30 miles east of the MN/WI border on 94, and only about 3 miles south off the interstate on highway 128. They have very good cheese curds, and aged cheddar. It’s out in the middle of nowhere and the shop is always crowded when I stop in.