By ANN LANDI

Lucin, Utah

The first key to understanding "Sun Tunnels," Nancy Holt's 1976 landmark of the Land Art movement, is to find her work from that heroic and grandiose period in American art. Recently, I joined two friends at the end of their tour of Land Art monuments—an itinerary that included Michael Heizer's "Double Negative," Walter De Maria's "Lightning Field" and Robert Smithson's "Spiral Jetty"—and we headed north from Salt Lake City, past the dreamy blue expanse of the Great Salt Lake and miles and miles of blindingly white salt flats. Then our rather primitive directions to "Sun Tunnels" took us east on a two-lane highway through scruffy desert terrain, distantly rimmed by pale violet mountains. The only serious sign of human habitation was the town of Montello, Nev., (population 193), where the ancient postmistress gave us vague directions to the ghost town of Lucin and the TL Bar Ranch. We never did find the ghost town, but spotted signs for the ranch and discovered a small sanctuary for migratory birds. Then, alternately squinting and peering through binoculars, I spied something that looked a bit like a pair of manmade semicircular humps in the distance.

We turned left onto a dirt road and after a mile or so along a route that looked not to have seen much traffic since covered-wagon days, we arrived at four massive concrete pipes that could pass for the construction site of some alien life form. We had arrived.

Barbara Rachko

Nancy Holt's 'Sun Tunnels' (1976) sought to bring a human scale to the vast Utah desert.

Each of Ms. Holt's four tunnels is about 18 feet long and 9 feet in diameter, and as we scrambled inside, my first impulse was to pose as Vitruvian woman—arms and legs outstretched to approximate the Leonardo drawing—inside one of the apertures. The tunnels were raw-looking against the parched landscape and achingly beautiful sky, and our initial reaction was a shrug of the shoulders: "What's the big deal?" They're lined up in an open X-construction and, according to my background notes, each weighs 22 tons and rests on a buried concrete foundation; a rectangle drawn around the perimeter of the monument would measure about 68 feet by 53 feet, and the wall thickness of each tunnel is 7 inches.

So much for the dry facts. As we explored the interiors, magical things happened. The tunnels were about 20 degrees cooler inside than the midafternoon desert, and each has a different configuration of holes, from seven to 10 inches in diameter, corresponding to four different constellations—Draco, Perseus, Columba and Capricorn. The holes cast ellipses of light on the interiors, which change positions as the sun moves throughout the day (one wonders what the effect would be by moonlight). Each hole also acts like a kind of oculus—framing bits of the landscape—so that through one you might see a snatch of blue sky and scudding clouds; through another, a roundel of purplish mountains. (In intense heat, I had read in Ms. Holt's descriptions of the work, mirages can make these appear to be reflected upside down.) The larger openings at the ends also act like framing devices, so that from the interior you might have the illusion of standing inside a giant telescope. In all, the experience could prove both disorienting and intimate, affirming Ms. Holt's stated desire to "bring the vast space of the desert back to human scale."

Ms. Holt, now 74, is one of a group of artists who, in the late 1960s and early '70s, brought outsize ambitions to carving up, embellishing and taming large expanses of Mother Nature, whether tunneling into an extinct volcano (James Turrell), orchestrating celestial extravaganzas out of lightning (Mr. De Maria), or building a phantasmic city in the desert (Mr. Heizer). She is the widow of Smithson, who died in a plane crash in 1973, and arguably the only woman to have achieved prominence in the Land Art movement. She began her career as a photographer and video artist, and has long been fascinated by constellations and nature's light (for example, a work called "Dark Star Park" in a bleak stretch of Rosslyn, Va., just across the river from Washington, D.C., emerged from her musings about the deaths of stars, including our own sun).

I talked with Ms. Holt a few weeks after my "Sun Tunnels" visit to ask some questions about her monument, one of which was why she—born and raised on the East Coast—became so enamored of this particular site that she bought a 40-acre parcel in 1973. She has written about first visiting the desert in 1968, with Smithson and Mr. Heizer, and connecting with that kind of "Western spaciousness." When she found the terrain for "Sun Tunnels," she says, "I had the sense that I was perhaps walking on a piece of land that nobody had ever walked on before—the natives who lived there hundreds of years ago, I'm sure they didn't step on every piece of my 40 acres—and that was thrilling to me."

I also did not quite understand the positioning of the tunnels, and I'm still not sure Ms. Holt's explanation makes sense, but I throw it out there for the more astronomically sophisticated: The work, she says, "marks the yearly extreme positions of the sun. On the equinox, the sun sets and rises due east and due west, and then for the rest of the year, the sun is a little bit to the north or south." According to Ms. Holt, "Sun Tunnels" will yield a different experience according to the time of day. "If you get there at noon, you won't see any of the golden glow that comes through in some of my photographs, because that only happens when the sun is setting," she explains. "It's wonderful to sleep out there. Even with no moonlight, just under the stars, it's great."

And lastly, I wanted to know about some strange markings we found inside the tunnels—repeated striations, dark staccato lines. "No one's been able to give me a good explanation," she says, "but we think it may be guys shooting guns in such a way that the bullet spins around inside. You cannot keep a Western male from shooting a gun. It seems to be an impossibility." But she's rather pleased that the source of the markings remains unknown. "I kind of like the mystery."

And that's all of a piece with "Sun Tunnels" itself, which leaves one wondering what visitors hundreds of years hence will think of the work, as we wondered about the origins of the Pueblo ruins in Mesa Verde National Park a couple of days later.

But first they will have to find it.

Ms. Landi writes on culture and the arts.