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A “Must-See” Day Trip from Austin: The Inner Space Cavern of Georgetown

About thirty minutes north of Austin, Texas lies a fantastic cave called the Inner Space Cavern. I went there in early June while my husband attended a conference (read the Austin blog here). The cavern lies at the beginning of Texas Hill Country, near the town of Georgetown (I’ll blog about Georgetown next).

The building entrance to Inner Space Cavern looks unimposing from the outside.

Cavern-Tour Basics

Tours are offered multiple times a day, every day except major holidays. I showed up and joined a group of about twenty people. The tour lasted an hour and was led by two young men (one in training) who did a great job entertaining us, giving us facts, and allowing quiet spaces for us to take it all in.

Passageways between rooms were lined with heavy-duty mats to keep us from slipping on the moist, slightly muddy, floor. Electric light gave us just enough light to appreciate the rooms, and the guides carried flashlights. There were also safety rails installed in strategic places. I felt completely comfortable the entire time. Plus it was much cooler than outside! The inside of the cave is a constant 72 degrees, but humidity makes it feel like 80 degrees.

Electric lights shine on some of the features within each cavern room.

The Cavern’s Discovery

The cavern was discovered in the Spring of 1963 when some highway engineers drilled six-inch core samples to see if the ground was stable enough to support a highway overpass. One drill went through the ground and they could tell there was a big emptiness below. They followed up by drilling a man-sized hole and sent in some people to start exploring. On the tour, we got to see both the original discovery hole and the larger entrance hole in the ceiling of the first room ever explored.


The black hole in the ceiling is the original entrance hole to the cavern.

Features of the Limestone Cave

The Inner Space Cavern (whoever named it thought the cave’s features looked like landscapes on other planets) is a limestone cave. It’s many remarkable features, like stalactites (they hold tight to the ceiling) and stalagmites (they might reach the ceiling), and columns (formed by stalactites and stalagmites meeting somewhere in-between) are formed by a natural process that I will attempt to explain. Any mistakes in the telling are mine.

Ground water (from rain)–which includes carbon dioxide, mixed with decaying plant material (more carbon dioxide) and complex organic acids (humic acids)–seeps into the ground, slowly dissolving the limestone beneath it. This process leaves deposits of dissolved calcium carbonate, which often includes other minerals. The water continues to drip from the ceiling onto the cave floor, leaving deposits of calcite crystals. Over eons, they naturally create cave formations called speleothems. Here is a good blog  and another blog that briefly explain the different formations you might see in a cave.

During our tour, we were quiet for a moment to see if we could hear any cars driving on the highway overpass above our heads. You can’t hear cars, but we did hear an 18-wheeler, sounding very muffled, rumble overhead. But I did not care to hear the trucks, I was much more interested in listening to the constant dripping of water all around us. Speleothems  were forming as we stood there! I wish we could have stayed quiet longer.

Formations of straws, stalactites, stalagmites, and columns made up of gazillions of calcite crystals.

Bats in the Inner Space Cavern

There were a few incredibly cute bats in the cave too (Yes, bats can be cute). They were called Tricolored bats. They are tiny, and like to hibernate singly. This one was on the wall behind us. It could have easily fit into the palm of my hand. I think they should sell plush tricolored bats in the Inner Space gift store!

Tiny ears at the bottom, little legs at the top, wings peeking out the sides, and a brown furry back make this bat adorable!

Absolute Darkness

At the end of the tour, our guides led us to another fantastic room and asked us to sit down on a low rock wall built as a seating area. He told us he loved being in this cave, because here he could experience absolute darkness. Then he turned out the lights. Of course the lady next to me still had her cell phone on, so I asked her to turn it off, then we experienced absolute darkness.

It was amazing. I couldn’t see one smidgen of light, nor my hand in front of my face. A few kids called out, “I’m scared,” but they didn’t cry. Our guide started talking, which was good, because I felt a thrill of fear too. Imagine being stuck seventy feet down in total darkness!

A Light Show

Next, the guide took out an ultraviolet light and shined it on some cave formations. He showed us how the calcite crystals lit up like fluorescent lights on the limestone features. Then he took out a regular flashlight and made “drawings” on the limestone surfaces. He told us how the emitted light lingered after being absorbed; and it was true, we saw his drawings fade away like the grin of a Cheshire cat. When I got home, I called and talked to someone at Inner Space Cavern to ask about this process. I also looked it up. I’ll try to explain it here, hopefully my simple explanation is accurate!

When light is directed onto the limestone formations of a cave, it is absorbed by calcite crystals. This causes electrons within the crystals’ molecules to jump around in an excited state. As the electrons relax (slow down), they emit light energy. This process is called Photoluminescence. There are two basic kinds of Photoluminescence: Fluorescence which immediately re-emits light after absorbing it, and Phosphorescence which re-emits light at a longer wavelength than was absorbed; in other words, the light lingers longer. And here I will stop my simple explanation before it gets too complicated for me!

Pools of water, sticky mud, and speleothems, create a fantastic world within the Inner Space Cavern.

Fossil Finds and Tours

Much paleontology research has taken place from fossils discovered within the Inner Space Cavern. In fact, a paleontologist from the University of Texas is currently excavating and researching finds withing the cave. In the Autumn, he will lead monthly Ice-Age Tours of the cave where he will explain his findings. I would love to go on one of these tours!

Other tours are offered at Inner Space Cavern, including the one-hour Adventure Tour (the one I took), the 1.5 hour Hidden Passages Tour (flashlights only), and the four-hour Wild Cave Tour (die-hards only). Prices are reasonable, the guides are great, the cave is unbelievable, and the building headquarters offers snacks, restrooms, water, and has a nice gift shop. What more could you want? For more information, visit their website.



  1. Jeannine Thompson Jeannine Thompson

    The Tricolored Bats as plush toys need to be in their gift shop! So cute!
    What a magical place, Inner Space. Thank you for reminding me that stalactites hang from the ceiling and stalagmites grow upwards on the ground. I actually discovered a great way to remember this while reading your post. Stalactite has a “C” for ceiling, stalagmite has a “G” for ground.
    Thank you for the great photos and easy-to-digest scientific nibbles about the properties of light absorption and emission within a cave. What a magical place!

    • KarenGough KarenGough

      You’re welcome Jeannine! And you worded the scientific properties better than I did – next time I’ll ask you to write that bit! 😁 Oh, and it turns out that that they usually carry plush bats, but they’ve been having supply issues.
      Thanks for commenting!

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