Any good ideas for a 4 day road trip vacation for 2 adults? 

Well, that is pretty broad. What do you like to do? How much time are you willing to spend on the drive? What kind of budget are you looking at? 

If I had 4 days I'd drive down to Corpus Christi. 

Drive to Florida :) 

Well I have 4 days total, we like outdoor activities. Just trying to think of something different. Corpus Christi does sound like a good idea 

The hill country is nice too and not too far. The old chain of lakes is less than an hour away, I'm getting there someday! 

Thanks, great ideas. 

4 Days isn't too long. I think I'd head to Austin and spend a night there and then go to Fredricksburg. 

The old chain of lakes is less than an hour away,

Nice place - just wish they still allowed camping.

San Antonio - river walk is nice as well. 

San Antonio. Easy drive over, lots to do in the vicinity, easy drive back. 

Big bend?