I suggested that they should stop by Monahans Sand Dunes State Park if they take the northern route on I-20, or if they take a southern route combination of I-10 and cross-country driving, to try for Caverns of Sonora. Either one is an easy side trip from the highway. It's nice to get out of the car for more than bathroom stops, meals, and gas when you're making a long trip!

SRS