The Wave Pool. Quite a popular place for me in my teens, only to be left unvisted from ages 18-34. Well, that streak has been broken, and the good times I had as a teen are continuing!
First off, this has to be one of the cheapest ways to spend your day. $6 admission for Allegheny Residents (they do take cards or cash for your admission fee), $5 bucks to rent a tube $1 back upon return (cash only), and a plentiful snack bar with most goodies under three bucks.
While you technically are not supposed to bring in any outside food or drink, there is no one inspecting your bags, so I usually bring in my own snacks. The AstroTurf surrounding the pool can be a little rough, so make sure to bring a towel or chair. Because this pool is so big, it can accommodate a large crowd. I recommend arriving right at opening (11:30) to secure the best sun-bathing spot.
Don't forget the sunscreen!