Caverns of Sonora
About halfway between San Antonio and Big Bend National Park, well, there's a lot of open space that'll have anyone traveling I-10 saying, "Damn, we're STILL in Texas?" But a stop at these caves makes a nice break. Carved out of a massive limestone deposit by acidic water from an underground aquifer, the caves boast one of the most heavily concentrated collections of helictites in the world. The cool, two-mile walk will take you past the butterfly -- two helictites that share the same attachment point -- and the "snake pit," a room with so many twisting helictites, it looks like a pit of petrified... snakes! What'd you think we were going to say, onyx?