Wisconsin Dells has some of the largest water parks in the Country. I took my family there last year, some great slides.
If he’s interested in white water, there’s some great rafting and kayaking on the Wolf and Peshtigo rivers in northern Wisconsin. Wisconsin’s also one of the greatest of the Great Lakes states. He should check out Door County, Washington Island and all the great sailing, fishing, and biking that’s available up there. I’ve done all the things there that I’m talking about, having moved to Tennessee about 20 years ago from the Milwaukee area, where I’d lived and worked for the preceding 12 2/3 years.