Tubing the Guadalupe is what people come to the Hill Country to do in summer, and Kerrville is one of the better spots to do it. The river runs clear and cold over limestone gravel, fed by springs, and rarely gets warm enough to be unpleasant even in July. Several outfitters near town rent tubes and shuttle you upstream for a float back — a couple of hours depending on water levels, with enough current to keep you moving without much effort.
The river is lined with cypress trees whose roots reach into the water, and the limestone bluffs above give the whole stretch a characteristic Hill Country look. Weekends in June and July are crowded; go on a weekday if you want a quieter float. Closed-toe shoes or water sandals are useful — the bottom is rocky in places — and sunscreen is essential.