From I-35 take exit 206 and head west towards Texas State University-San Marcos. After Post Road there is a railroad crossing.  Just after the track turn right onto West Laurel Street.  There is a large sign above the road that says Aquarena Center.  The entrance is across from Bobcat Stadium on the East side of Aquarena Springs Drive.  Continue over the low water bridge until reaching a Y in the road.  Turn left and then take the first drive  on your right to the parking lot. There is a sign that says "Glass-bottom Boat Tickets". To purchase Glass Bottom Boat tickets and to get information about the park enter the first set of double doorsat the Texas Rivers Center adjacent to the headwaters of the San Marcos river.