Hermann Park is a rare and great grassy, shady area in Houston that everyone can appreciate. The space is huge and there's always something new to explore, from the tree-lined paths to the numerous play sets with plenty of swings and slides (and be honest, they're not just for kids).
Go hand out with friends during the day, take your kids to play in an afternoon, or go on an evening walk for a unique (and cheap!) date. Just be aware that the park does close at night and that if you're there after closing, security will ask you to leave, which isn't a bad idea.
Pros: Good parking, lots of stuff to do
Cons: Can get a little shady at night