Round Top is located at the eastern edge of the Texas Hill country -- it's about a 2-hour drive from Houston, and about a 90-minute drive from Austin:
Come out 290 towards Austin. After you pass Burton (about 12 miles west of Brenham), exit on highway 237. This is a left-hand exit. It is marked La Grange/Round Top. Head south on 237 about 8 miles to Round Top.
Come out 290 towards Houston. After you pass Ledbetter, you'll see a sign for Round Top Road (the road before it is Deer Haven Road). Turn right and follow the road into Round Top.
Come out 71 to La Grange. Exit at highway 159. Go left under 71, and head north on 159. Just past Oldenburg, 159 will meet 237. Continue heading straight on 237 (159 turns right to go to Fayetteville). Proceed north about 9 miles to Round Top.