It never failed, since I was 7 my family and I would take two certain trips every year in Wisconsin... camping and the Dells.
Looking back on them as a teenager now, I have more memories from those three day weekends then I do on some of our larger family trips. What's perfect about the Dells is that it seriously has something for everyone. Petting zoos, roller-coaster and other rides, go-karts, miniature golf, and some of the biggest and best water parks in the world; but what really sets the Dells apart from all others is that there are multiple areas of these things. If one petting zoo is too packed go across town to the other one. Don't like one water park, go to another one, they are all over.
Of course there are a few things the Dells are really known for, like their half car/half boat rides called ducks (highly recommend taking a tour), a petting zoo/ deer park that is like no other, and their downtown strip of shops, eateries, and entertainment. The downtown area is great for people watching and the people who visit are friendly for the most part. Also I've been here many times since with just friends and we've all had a lot of fun.
Oh...here is a little Dells history which I found fascinating:
Wisconsin Dells was created during the Ice Age, which changed the landscape of Wisconsin. HH Bennett a Civil War veteran, come to photograph the natural beauty of the area. Bennett was a photographer and promoter, he was also a pioneer in photography and his famous photo of Stand Rock, with his son, Ashley, caught in the middle of a jump, was at first thought to be a fake. An action shot like that did no seem possible with the cameras at that time.
Check it out for yourself.