This attraction used to be great and it probably still is - but now it requires that you buy a ticket to the Valleyfair amusement park AND pay extra for the activities.
I went here a few times because the mini golf course is great and I love the bumper boats and go-karts. The last time I was there you could go into Challenge Park without paying for an admission into Valleyfair. You would just have to pay for parking.
Now to me it is definitely not worth paying admission into Valleyfair and paying extra for these attractions! It is strange that they would change this - I assume they have lost a lot of business based on this change.