Quoted By:
Garner State Park
Krause Springs
Enchanted Rock State Natural Area
Colorado Bend State Park
Lost Maples State Natural Area
Padre Island National Seashore
Big Bend National Park
Coloardo bend is probably my favorite. You can canoe up and down the river and see a bunch of waterfalls and there's an awesome spring/swimming hole there too. Gorman Falls is amazing too.
My suggestion is to do a graduation road trip and hit a bunch of places.