Jacob's Well in Wimberley, Texas. It's a significant karstic spring, the largest perennial spring in the Texas Hill Country. It flows from the most extensive underwater cave in Texas. 4m diameter mouth cave, descends vertically for about 10m, continuing from there at an angle as a series of chambers separated by narrow, often deeply silted and unstable necks, ultimately reaching a depth of at least 40m.
What's the ONE thing you must do in Texas, according to the Huffington Post? Tube the Guadalupe River! Nothin' says Texas like drifting down the river on a toasty summer day with all your best friends and a massive floating cooler of Coors.