Should you ever find yourself driving in Texas’ hill country, you’d be well advised to spend a few hours visiting the Natural Bridge Caverns, just north of San Antonio. It’s got a beautiful selection of cavern geology (stalactites and stalagmites and such), it’s a pretty easy walk, and photography is allowed / encouraged.
Oh, yes — and there’s a limestone natural bridge, seen here at the cavern entrance, over the shoulder of our guide.
The Texas hill country gets its nickname from the fact that it’s karst terrain — starting with limestone beds laid down millennia ago (when this part of North America was an ocean floor) which were subsequently uplifted, then underwent underground erosion by ground water. Many of the caverns formed in this process have collapsed, leaving a hilly surface for modern residents.
The Natural Bridge Caverns formed about 140 million years ago, were discovered in 1960, opened to the public in 1964, and tours have since been given by the family owning the land they reside under.
The developed part of the caverns have over a half mile of paved trail, and extend to some 260 feet below the surface. The caverns are considered to be “alive,” with features still growing.