Inner Space Cavern

Inner Space Cavern was found by accident. In spring 1963 a Texas Highway Department core-drilling team was testing the ground for a highway crossing when its drill bit dropped 26 feet into a void. The Texas Speleological Society then won permission to explore it, entering through a wide hole drilled into the roof of one room, and by the end of the first few days had surveyed more than 7,000 feet of passage. The cave opened to the public in the summer of 1966.

It lies in Edwards Limestone, and the Handbook of Texas calls it highly decorated and complex, with about 95 percent of it still active. The Handbook records a large variety of late Pleistocene vertebrate fossils, recovered from two natural entrances that have since been filled; the cave's own site refers to prehistoric animal bones. The Handbook describes the present entrance as an artificial tunnel with a cable car. The passages range from tight crawls to large rooms, and the mud is sticky throughout.

The cave stays at 72 degrees all year and, its operators say, does not flood in rain. Tours leave about every 20 minutes. It is open daily, 9 to 4 on weekdays and 10 to 5 on weekends, except Thanksgiving, Christmas Eve, Christmas Day and Easter Day. Same-day tickets are sold at the cave. The address is on the I-35 frontage road, and the site's own map link disagrees on north or south, so check before you drive.