Aquarena Springs Eternal
A feature of the Balcones Fault, which runs roughly along the alignment of Interstate 35 through Texas and divides the Hill Country from the plains, the San Marcos Springs emerge from the ground twenty feet below the surface of the water, ice-cold and so crystal clear that you can see the sand bubbling below the glass bottom of the boat.
In fact, many tourist attractions are the Balcones' fault* - Natural Bridge Caverns in New Braunfels, Wonder World in San Marcos, and Inner Space Caverns in Georgetown, to name a few.
The Meadows Center for Water and the Environment (formerly known as Aquarena Center, formerly known as Aquarena Springs) spent many years as a seminal Texas tourist attraction. It's now run by Texas State University in San Marcos as an environmental conservation site. This is a somewhat different fate than what was envisioned by an earlier owner, pictured above.
Only the building on the far bank of the river ever actually existed, and still does; a former resort hotel, it now serves as The Texas Rivers Institute. You can still take a tour on a glass-bottomed boat. But Ralph the Swimming Pig**, the mermaids, the submarine theater, Johnny Weismuller, and wanton disregard for nature are things of the past - at least, at Aquarena.
But it is a pity that the submarine theater's gone. It looked sort of like a big, rusty Airstream trailer, and was removed only a couple of years ago after resting, skewed and abandoned, halfway in and halfway out of the water. Back in the day, you see, you bought your ticket and entered the theater above water. It then lowered beneath the surface so you could watch the mermaids do stunts, like sipping a drink. This is not particularly impressive under normal circumstances, but under water that shit's dynamite.
It's a beautiful place, and a good thing the visionary entrepreneurs of the 1950s didn't succeed in paving it over.
* I'm so terribly sorry
** I don't know if any special training was involved in this. I think swimming is just what pigs do if you toss them in the water. Not that I've tried.