The Day Tripper (a regional PBS show where a dude travels to a city and spends a day there doing stuff) filmed in San Marcos earlier this year.
http://thedaytripper.com/daytrip/san-marcos/
The clip is about 30 minutes.
As most of you know, San Marcos is 30 minutes from Austin, 45 from San Antonio. Coming in you can hit both of those cities if you want.
However, you can find plenty to do between the cities that will give you a real feel of the Texas Hill Country.
San Marcos River-
Some of the state's best freshwater swimming holes (Guadalupe, San Marcos, Blanco Rivers are close by)
Texas BBQ Trail
BBQ is religion to us, but if you want to experience some of the best Texas BBQ, you can find a plethora of places within 30 miles of San Marcos
Texas Craft Beer and Wine Scene-
New breweries and brewpubs are popping up all around the area. San Marcos along with neighboring towns New Braunfels, Canyon Lake, Wimberley, and Seguin are all producing beers and wines.
http://texasbeerguide.com/breweries/