Just show up. Look for the Missions Trails signs on the Interstate and follow them. Once you find Mission Conceptsion they have a ranger station there and you can see a map for the rest of them. They are not too far apart. They (the interiors are open 8a to 5p 6 days a week and a few are open on Sunday as a parish church. Good luck, call me when you pass through town. Just take I35 south to Denton and then take I35 w south thru fort worth. It is just a 300 mile jaunt to San Antonio from here.