Barton Springs Pool. When those summer days get hotter than a potter's furnace, dip into Zilker Park's 300-yard-long, spring-fed swimming pool, a favorite with locals. The clear springs produce from 12 million to 90 million gallons in any 24-hour period, the water always a rather cool 66° to 70°. Zilker Park, 2201 Barton Springs Rd. 512/476-9044. www.ci.austin.tx.us/parks/bartonsprings.htm. Free (Nov.-Mar.), $3 rest of year. Hours vary. Closed 3 weeks in Feb. and Mar. for spring cleaning.