San Antonio is a great place. Half of my family lives out there, so I grew up going but not usually doing the tourist stuff. The Riverwalk is beautiful by day but especially at night.
The thing that has always been of note in SA, to me, is the food. Go to a Mexican bakery and get the sweet bread or pan dulce. Oh, and have a breakfast taco, too. Eggs with chorizo and potatoes. Yum!