There is plenty to do in Marble Falls. Or Not. You can enjoy water sports or just float along the lakes, or partake of the dining and seasonal festivities. The shopping is fun when hunting for that antique or one of a kind item. It sits in close proximity to Austin, Georgetown, and Frederickburg. Making them great little day trips.
Here are some links to more information to help you plan your stay.
Visiting Marble Falls: http://www.ci.marble-falls.tx.us/35/Visiting
Things to Do in Marble Falls, TX: https://www.tripadvisor.com/Attractions-g56229-Activities-Marble_Falls_Texas.html