San Marcos sits on I-35 in the Texas Hill County, about 40 minutes southeast of state capital Austin. San Antonio is also pretty convenient to San Marcos. Head about an hour southeast on I-35 to reach it. The clean, warm San Marcos River provides plenty of options for water recreation right in the city. Head to Rio Vista Park for particularly fun tubing or kayaking. Rio Vista Falls Dam is the area's centerpiece. Shoot the rapids and get extreme with a trip over the falls! You've got a couple of options if you're coming to the area via RV. Canyon Trail RV Resort provides 76 full hookup spaces along with free Wi-Fi (service can be spotty, though). Head to Pecan Park Riverside RV Park for 116 more big-rig friendly sites. Pecan Park also features an extremely relaxing Jacuzzi-tub area. Note that neither park allows for tent camping, though. Keep in mind that Texas summers get very hot. You'll be dealing with temperatures in the mid-90s from June to September. Aim for spring if that doesn't sound like a good time to you! From March to May, highs average a more comfortable 80 degrees or so.