It’s a typical weekend in the upscale neighborhood of Oak Park, three miles from the San Antonio airport, and the shopping center off busy Nacogdoches Road is filled with customers milling about. They leave the dry cleaners, finagling with the blowing sheets of plastic around skirts and suits, and load cars with groceries from H-E-B. Outside Starbucks, a group of women laugh on the sunny patio. Just a few blocks away, a wrought-iron fence surrounds a small plot of land between Camellia Lane and Hillview Drive. Oak leaves blow around signs identifying prickly pears, Alamo vines, and mountain laurels. 

You’d never know it, but beneath this spot lie more than five thousand feet of subterranean mazes. One of Texas’s first show caves, the place once hosted fortune tellers, dance performances, and a zip line. Over the centuries, it’s been visited by amateur spelunkers, scientists, and more than a few sneaky teenagers. This cavern is home to at least two endangered species that live nowhere else on earth. More recently, Elon Musk even entered the picture. Welcome to the Robber Baron Cave.

The oldest known graffiti in the cave dates to 1836, although it’s likely that Texans have been exploring this spot for much longer. Many of them have needed to be rescued. In the 1920s, two schoolboys were lost here until a search party located them late at night. In 1925, agents from the Bureau of Prohibition led an ill-planned underground raid here; they found no booze, but were lucky to come out with their lives after being trapped inside for more than three hours. A map from 1921 shows the cave’s long, winding tunnels and rooms with such colorful names as the Undertakers Parlor and Gypsum Alley. Early rumors held that it was a passageway to China or the Philippines. In 1929, a Dallas Morning News reporter amplified the mythology of the place, writing breathlessly, “If these walls could talk, they . . . would reveal tales of crime which cause the blood and thunder stories of the Wild West to pale in significance.” 

Robber Baron Cave San Antonio
The sinkhole entrance to the cave in 2011.Joe Mitchell/Texas Cave Management Association

The facts are these: Robber Baron Cave is the longest cave in Bexar County and the second-oldest commercial cave in Texas. According to the Texas Cave Management Association, a nonprofit that manages the cave, it formed about two million years ago. The sinkhole entrance is lined with lush ferns forty feet below a footbridge. Two spiders that live here—the Robber Baron cave meshweaver and the Cokendolpher cave harvestman—have been found nowhere else. In the summer, rats and raccoons escape to the cave’s cool limestone depths; in the winter, tricolored bats curl up here to hibernate. In 2003, the U.S. Fish and Wildlife Service designated about a thousand acres of caves in Bexar County, including Robber Baron, as a critical habitat for seven endangered invertebrates.

In the beginning of the twentieth century, the Robber Baron Cave was the site of lively subterranean dinner parties, with guests dancing to “Sweet Georgia Brown” and “West End Blues” on a portable Victrola. Boy Scout troops held fish fries on the land above, where there was a small park with a merry-go-round and vendors who sold food and drinks. In 1910, a prominent local businessman named George Saur purchased the property and hired Arthur Harp, a marketing whiz from Kansas, who gave the cave its intriguing name. It had previously been known as the Cave of the Quebrantahuesos, which translates to either “the cave that breaks your bones” or “the Vulture’s Cave.” 

Saur and Harp set about turning the cave into a tourist attraction. They filled the V-shaped entrance with rock and soil to create a path, built a wooden staircase to an area outfitted with benches and lighting, and excavated the tunnels around the entry. When preparations were complete, Harp, a natural storyteller, painted an ad on the side of his Whippet pickup and drove it around town. He told tall tales of “bloody-thirsty Injuns,” hiding monks, and ghosts out for revenge. The media loved the myth of an underground lair for villainous activities, with the El Paso Herald writing in 1911 of “sudden descents on peaceful travelers, of plunder and rapine, and of dragging prisoners to the cave for their final dispatching.” (It seems journalistic fact-checking standards were a little looser back then.) 

When the cave first opened for business in 1923, visitors lined up to pay fifty cents for entry, and the next decade saw more than 300,000 visitors. But the stock market crash in 1929 brought tourism to a standstill, and interest around the cave eventually dried up completely. By 1933, the cave’s days as a tourist attraction were over. Arthur Harp moved back to Kansas and didn’t return. 

Robber Baron Cave San Antonio
A passage through the cave in 2008. James Jasek/Texas Cave Management Association
Robber Baron Cave San Antonio
Two men pose as robbers in the cave in 1923. Harvey Patteson/Texas Cave Management Association

Since 1995, the cave has been managed by TCMA. According to its website on Robber Baron, the nonprofit “attempts to balance protection of the cave with education, science, and recreation while being part of the neighborhood it resides in.” In the early 2000s, the group—along with Bexar Grotto, the local chapter of the National Speleological Society—began a mission to restore the cave. Volunteers removed trash and non-native plants, and they built an iron gate to create a more natural flow of organic matter and water into and out of the cave. San Antonians pitched in to build picnic tables, mend fences, and install a gravel path from the alley entrance. Then guides once again brought scout troops and other eager explorers to tour the cave. Lindsey Adamoski, who has led multiple expeditions into the cave, calls Robber Baron “an adult playscape.” “I love that cave very much,” she says. “It is a special place.”

Special, but not always safe. In 2018, a teenager on a field trip got stuck in a spot known as the Hole in the Floor; firefighters pulled her out after a lengthy struggle. The cave was closed to public exploration in 2020, and according to Michael Harris, a biologist and TCMA staffer who manages the cave, there are no plans to reopen it. “We are taking this time to do some sampling and more scientific research,” he says.

Robber Baron has been the site of significant controversy in recent years. In 2020, an alleged sewage spill into the cave prompted an inquiry from the Texas Commission on Environmental Quality. Then Elon Musk entered the picture. Musk wants to build underground transit tunnels in Texas, and his Boring Company is in talks with the Alamo Regional Transit Authority to build a loop that would connect the city’s airport and downtown. No route has been released, but the tunnel would run through a region whose delicate karst ecosystem is home to numerous endangered species. The TCMA and the Texas Speleological Society sent a letter last May to the transit authority voicing “major concerns” about the plan. “It doesn’t make sense to run a tunnel through a karst area,” TCMA president Jim Kennedy told the San Antonio Express-News, calling the project “extremely problematic and very expensive . . . It’s like trying to put a tunnel through a sponge.” Kennedy declined interview requests, citing “ongoing litigation.” Via text message, he wrote, “The cave is a unique Texas treasure, particularly because of its hypogenic formation but also because of its length and biota.”

Though the cave itself is off-limits these days, the property functions as a public park. On a recent Sunday, a family ate lunch on a picnic blanket on the lawn. Their golden retriever sniffed around the mesquite tree at the top of the staircase that leads to the sinkhole below. A metal sign was nailed to the mesquite’s trunk: “Caution! Falling rocks. Sinkhole walls may be unstable. Enter at your own risk!” The parents called for the dog’s return as the kids nibbled at sandwiches, the history of what lay beneath far from all their minds.