If you want to "drive around" and see some scenery Galveston is only like 45 minutes away from most parts of Houston.
Something my son loves to do if you want to avoid the zoo crowd is go to the Arboretum......it's a bunch of nature trails just inside the loop (real close to the Galleria so it's perfect for before or after shopping). We were just there last weekend and there are already lots of leaves on the ground, turtles, birds, etc............it's almost like you aren't even in Houston!