Somewhere around 20 million years ago, the coastline of present-day Texas settled, creating a series of faults and cracks through which water flowed and carved out a vast system of underground caves. Thanks to the discovery of ancient arrowheads, spearheads, and human teeth, modern day scientists believe those caves were inhabited by early humans seeking shelter. Those same caves now serve as a playground for the grandchildren of Bob and Denise Schubert, after the San Antonio residents discovered a tiny access point to the caverns on the edge of their property line.

In 2004, Bob and Denise bought a plot of land in a gated subdivision less than two miles from Natural Bridge Caverns in San Antonio, Texas—the state’s largest-known commercial cavern, open to visitors nearly every day of the year. That same year, Bob was walking around his new land and noticed the weeds blowing in a breeze that seemed to be coming from the ground. Upon further investigation, Bob found a small, one-inch blowhole in the patch of earth—an indication of a possible cave below. The Schuberts brought over a geologist from the nearby Natural Bridge Caverns and had him investigate. His findings confirmed their suspicions: The land the Schuberts had just purchased was likely sitting right on top of a natural cave.

Perhaps none of us would know about this private-access cave if the Schuberts hadn’t recently put their home on the market, where the $875,000 listing, which begins, “Do you love Natural Bridge Caverns?”, was unearthed by the sleuths at Zillow Gone Wild. According to Zillow data, the four-bedroom home has been viewed more than half a million times, and saved by nearly 9,000 people. The house itself is lovely—a 2,700-square-foot two-story with big windows, an updated kitchen, and a soaking tub—but nothing particularly out of the ordinary when it comes to expansive Texas homes. The definite draw is the added basement in the backyard, in the form of a 30-foot-deep cave.

On a recent visit to the Schuberts’ San Antonio house, Denise told me about how Bob’s 2004 blowhole discovery led to the construction of their private backyard cavern. Starting in 2006, the Schuberts spent 10 years hiring a series of volunteer geology students, geologists, and local amateur cavers to clear an entrance to the subterranean area a few dozen yards from the Schuberts’ home. By 2016, the Schuberts were ready to hire a professional excavation team to finish the cave, who, at one point, saw that the neighbors were having a swimming pool dug, and borrowed the construction company’s backhoe. Now, the Schuberts’ cave—called Park Caverns—consists of two rocky cave “rooms,” accessible via a staircase with lights and handrails that the Schuberts had installed below a trap door in the backyard. The private cave ultimately cost over $87,000 to excavate and finish.

Despite growing up in Texas, now living in Austin, and even previously residing in San Antonio for a year, I’d never personally been to Natural Bridge Caverns. It’s long been one of those billboards I drive by with little more than a passive acknowledgement, the same way I’ve always passed by the giant squirrel in Bastrop, the graveyard of monstrous Presidential heads in Houston, and every single Buc-ee’s. But when the opportunity arose to tour the Schuberts’ personal cave, I jumped at it.

Cautioning me to watch my head, Denise led me down 30-feet worth of stairs, first to the smaller of the two rooms, which is about seven feet wide, and then the main room, about 20 feet in circumference. She pointed out the cave’s sooty black rock, which, Denise told me, is evidence that bats lived there at some point. Classic. (When I asked why the rock would be black from bats, she explained that it’s from their droppings.) While it was nearly 100 degrees aboveground, the cave was dark and cool—according to Denis, it’s a constant 72 degrees year-round, so on cold winter days, it’s warm by comparison—and when we stood still, it was completely silent. For someone who isn’t claustrophobic, it’d be an extremely peaceful place to relax. As I admired rocks along the walls ranging in color from rusty red to calcium white, Denise called my attention to the patches of quartz deposits, which sparkled in the light from my phone’s flashlight. She also let me touch the cave’s rocky surfaces, which I imagine would’ve been a no-no at the official caverns up the street, as the oils on human fingertips can cause the rock formations to stop developing.

Back in the Schuberts’ bright living room, lined with west-facing windows that frame the Hill Country sunsets, they told me about how their grandchildren played in the cave during the five years that it was finished, how the geologists that visited their backyard over all those years taught them about the cave formation and rock features, and how to identify the possibility of even more rooms looming beneath the cave’s current floor. They speak about the cave like it’s just as much their home as the actual house. But when a recent opportunity to live near family in Maryland came up, the Schuberts knew their time with Park Caverns was coming to a bittersweet end.

To list the property, the Schuberts hired their friend and neighbor, Lori Largen. With the cooler market in Texas, the house sat on the MLS for a few weeks, and, discouraged by the inaction, the couple decreased the listing price by $75,000 in mid-July. But as soon as Zillow Gone Wild shared the listing, the Schuberts were bombarded with requests, even after the house eventually went under contract.

The four-bedroom residence sat on the market for a few weeks after the couple listed it, but as soon as Zillow Gone Wild shared the listing, the Schuberts were bombarded with requests." layout="wide" credit="Photo by Amanda Terry/Twist Tours" photoUserId=""/>

As Largen told me in the Schubert’s living room shortly after my cave tour, she didn’t have to do much to stage the house, with one notable exception: Remove the vast collection of really big rocks from the cave that the Schuberts had used to decorate the mantles and other parts of the house over the years.

“Bob really got into the rocks,” Denise said. “We had rocks in almost every room.”

Top photo by Amanda Terry/Twist Tours.

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