Saw your post regarding NYC-Philly...
Sounds like you are reconsidering San Antonio.

If staying in San Antonio, consider this book:
Day Trips from San Antonio, 3rd (Day Trips Series) by Paris Permenter and John Bigley (Paperback - Sep 1, 2006).

I have not read it, but I have used another book from the same series:
Day Trips from Phoenix, Tucson, and Flagstaff, 8th (Day Trips Series) by Pam Hait.

I also have used another book which discusses self-guided walking tours of Downtown SA, Riverwalk, Mission Trail, Ft Sam Houston, and various neighborhoods and parks:
San Antonio on Foot by Diane Capito and Mark Willis (Paperback - Mar 1998).

Absolutely take a trip out into the hill country-I love Luckenbach, Fredericksburg is a cute German town although I know it has become more touristy. Stay a couple of nights in Austin and the rest in SA.