Rainbow of the Heartland in Grimes offers open play on weekdays for $10 per child or you can purchase a punch card for a discounted rate. I was worried the play structures would be boring for my kids, but three of them were geared for older kids and my boys really enjoyed playing there today.
In addition to the play structures, there are two trampolines (one child allowed at a time). There's also an outdoor play area that's included in open play, but due to the cold weather today my kids only played inside.
There are a couple open play rules to be aware of. Closed toe shoes are required and you can bring food or drinks, but they're not allowed in the play area (only in the party room).