San Antonio is my favorite town. We went there for our honeymoon and I never wanted to leave. We almost bought a house there but in the end the family convinced us to stay in Chicago. You'll love it -- try to stay at one of the older hotels like the Fairmont (the hotel that was moved across the town). There's Mi Tierra for Mexican food, Shillito's Deli, La Villita for shopping, the Riverwalk and its shops. While you can stay around the Riverwalk, it's nice to drive around the city because it quite large. San Antonio is beautiful. I love old architecture and buildings (especially churches and cathedrals) and San Antonio has alot of this. Let us know how it goes!
