On SoHo’s cobblestoned Wooster Street, tucked above North Face and Lululemon boutiques stocked with neon athleisure, there is an otherwise empty, white, second-floor thirty-six-hundred-square-foot loft filled with 140 tons of dirt. It’s open to visitors from Wednesday through Sunday, noon to six P.M. The surreal aspect of its very existence is undercut somewhat by the normalcy of public access and consistent hours, as if it were a store selling nothing. Walking up the stairs and into the space on a recent late morning, I was first struck by the sensation of hush. It was not just the quieting of the sounds from the street but an enveloping cocoon of warmth and musty scent, like a field after summer rain. Around the corner, a raked expanse of soil two feet deep filled the loft from edge to edge, occupying what might otherwise be a bedroom and rising up to meet wide exterior windows.

This is The New York Earth Room, an installation by the New York–based artist and musician Walter De Maria, who died in 2013. De Maria was part of the 1970s Land Art movement that included such compatriots as Robert Smithson, of Spiral Jetty fame, and Michael Heizer, whose City is an enormous monument complex in the Nevada desert still under construction. Their work deals with massive scales, both in time and space. In October 1977, the German art dealer Heiner Friedrich hosted The Earth Room as an exhibition at his gallery, which then occupied the Wooster Street space, where the dealer also lived in a front apartment. The installation was meant to last for three months, but it never left, and in 1980, Friedrich helped found the Dia Foundation, an art organization that has pledged to preserve De Maria’s work in (more or less) perpetuity. This year marks the fortieth anniversary of The Earth Room’s quiet persistence, which Dia is marking with commemorative events and ongoing exhibitions of De Maria’s work.

De Maria might have created The Earth Room, but its public face is Bill Dilworth, a sixty-three-year-old abstract painter who has been caring for the installation as its curator for the past twenty-eight years. Walk into the back office room past the glass-protected aperture that opens out onto the field and most days you’ll find Dilworth behind a high wood desk. Tall, gregarious, and preternaturally youthful (a result of dirt therapy?), he has thought more about this particular piece than just about anyone. “My life and my experience here is immersed in art, earth, quiet, and time,” he told me. “It’s a continual growth of time.”

At least it used to be quiet. Over the past decade The Earth Room has seen an explosion of visitors. “There are days when not ten minutes go by without someone,” Dilworth explained. “Whereas in the early days we’d get thirty-five hundred people a year, the last few years it’s been sixteen thousand.” Every time someone shows up at the door, their image appears on a console screen at his desk, and Dilworth pushes a button to let them in—sometimes with a white wooden plank so he doesn’t have to reach so far. He chalks the increased traffic up to New York City’s larger changes—going from “wild to wealthy,” as he put it—as well as The Earth Room’s inclusion in the Lonely Planet guides starting around 2008. “They look at the book and they look at that and they just don’t get it,” he said, gesturing toward the installation. “A lot of people will walk right by it not knowing that’s it.”

De Maria himself stayed silent on the work’s significance, though it came at the peak of the artist’s career. In 1977, he also created the Lightning Field, a grid of four hundred stainless steel poles installed in New Mexico, and in 1979 the Broken Kilometer, five hundred two-meter-long brass rods laid in rows, installed at 393 West Broadway. Both are under the purview of Dia as well. De Maria described The Earth Room as a “minimal horizontal interior earth sculpture.” Accurate, but possibly unhelpful for those seeking a deeper message. Dilworth would rather let the piece speak for itself, too: “When people come up and ask me what it means, I really just turn them back to The Earth Room so they can look for that answer.”

Celebrating The Earth Room’s anniversary exposes a particular paradox as well. The piece is static and permanent, a place visitors can, and do, return to over the course of decades as a pilgrimage. Dilworth is at pains to keep it stable, watering and raking the earth (the same organic material installed forty years ago) on a weekly basis. “It’s very much a Zen garden. You maintain it and nothing grows,” he said. In fact, mushrooms and grass have sprouted, large dragonflies have hatched from subterranean nests, and a visitor even once threw a can of black beans on the dirt. Vigorous raking takes care of most intruders. Yet the context of the work is always shifting. As Bill says, “The Earth Room is meant to be unchanging; nevertheless it evolves.”

One such evolution is the texture of the earth. Dilworth began working for Dia in 1979, on projects with artists La Monte Young and Marian Zazeela and the board member Lois DeMenil. In 1989, he noticed the desk job at The Earth Room; two months later, it opened up and he nabbed it, despite the fact that it paid half his previous carpentry gig. The previous caretaker raked the dirt smooth; on his first day, Dilworth decided to do it with a cultivator, a spiked tool used for tilling farms. “It was just an effort to make it look more like earth,” he said. Initially, the piece had electric lights on above it, but Dilworth got into the habit of leaving them off, since natural light makes visitors stay longer. “If there are times I feel I’m getting inundated, I’ll flip the lights on.”

De Maria’s work is about sensory experience: the sheer feeling of being in the presence of so much earth. It’s grounding, in a literal and metaphysical sense. Dilworth sees a particular message coming to the fore more recently, however, about our increasing isolation from earth and our impact on the planet as climate change becomes more blatant. The way The Earth Room shelters a small parcel of dirt, keeping it fresh and protecting it, draws out our ancestral connection to the material. “It’s like a flag for preserving Earth,” Dilworth said. “It’s important that people understand it’s worth preserving, and this can remind them.”

Even as his job has stayed the same, Dilworth’s life has changed. He and his wife, Patti, who watches over De Maria’s Broken Kilometer, have raised two children in the Lower East Side loft they’ve occupied for decades and recently became grandparents. They’ve endured struggles for tenants’ rights and a luxury renovation when the building fell into the hands of developers. In 1996, the couple bought a house in the Adirondacks, where they stay for three months every summer while the installations close for maintenance. “I’d love to see an Earth Room out in the country,” Dilworth said. “That’s where the real balance is.”

No photos are allowed of The Earth Room, repelling what might otherwise become a horde of Instagrammers making their way up the stairs. What you take away from standing in front of the dark, musty expanse is what you bring to it. You leave knowing that you can always come back and the earth will be there just the same, only different.

Kyle Chayka is a writer living in Brooklyn. His first book, on minimalism, will be published by Bloomsbury in 2019.