Located just down the street from Kalahari, which bills itself as Wisconsin's largest indoor water park, Wilderness Resort also claims to be the biggest - not just in the Dells but in the whole country. That's because Wilderness is spread out over 600 acres, with myriad indoor and outdoor water parks, as well as a ton of other attractions. Each individual park is big, but when you put them all together, Wilderness is humungous.