Recommendation for Wisconsin getaway from Chicago?

I need a recommendation for a decent Wisconsin getaway that’s not too far from Chicago. Here’s the story: an author whose novel I’m translating with my colleague is visiting Chicago from abroad for a conference in early May. She and I want to get him out of the city after the conference for a night or two, show him something other than Chicago, and have a quiet place to go over our translation with him. (He’s never been to the US before.)

Any recommendations for a place that’s decent but not insanely pricey, maybe some nice walks in the area, and, let’s say, a max five hour drive? Thanks!