On the bus into the desert, I surveyed my fellow nuclear tourists, curious about what sort of person books this curious sort of trip. At the back of the bus, a gaunt, deeply tanned, white-haired, homeless-looking man got a whole row to himself. He looked like a combination of Gandalf the Grey and the guy who kidnapped Elizabeth Smart. Even though the forecast called for 100-degree heat, he wore a sun-faded lavender sweat suit, with a pair of cornflower-blue nylon basketball shorts over his sweat-bottoms. (I later learned, to my surprise, that he was a recently retired infectious-disease geneticist.) One of the few young men, a pale, skinny guy with a handlebar mustache and olive-drab combat fatigues, wore a T‑shirt commemorating the Chernobyl disaster. Nina Elder—a 31-year-old artist and the only unaccompanied woman on the tour—told me that her preferred medium was “radioactive charcoal,” and that she had signed up for the tour because she was creating a series of images of nuclear tests.

John Spahn, the retired government official who led our tour, said he’d had a number of nutters try to join tours in the past—including a man wanting to wear a full spaceman anti-­contamination suit. Spahn said the prohibition on cameras and phones was a precaution to protect sensitive areas and activities at the test site, including what he slyly referred to as “Area … something in the low 50s.”

We drove northwest, to Mercury, Nevada. About half a mile from Highway 95, we reached a gate with a huge white placard forbidding us to go any farther without permission. Spahn said that when wayward tourists or anti­nuclear protesters stray beyond the sign, security teams materialize from out of the desert. The nosy are merely turned back, but trespassing protesters get arrested—though they’re now charged on the spot and spared the hot, 150-mile paddy-wagon journey to the courthouse in Tonopah that they used to endure. Spahn said he had un­wittingly taken antinuclear protesters on tours, and the confrontations became heated. On this particular tour, no one sprang any surprises, although Gandalf handed Spahn a long list of handwritten questions, some of them suggesting that the test site might have been a cover for a secret gold-mining operation, or perhaps illicit government experiments. Spahn flipped through the list coolly, and Gandalf didn’t press the issue.

Past the gate, we proceeded another few miles into the hills that shield the test site from the highway. Mercury itself turned out to be a small company town, with a post office, cafeteria, and steak house but no permanent residents. (Employees of the test site commute in by bus—about 1,200 daily—and stay overnight, in simple dorms, only when necessary.)

We passed signs warning of contamination and forbidding the fool­hardy from pocketing soil or adopting pet rocks. Then the real show began. We stopped to check in at an office and submit to a head count. (If an incident occurs, Spahn explained, “they’ll need to know how many body bags to get.”) We then drove toward Bailey Bridge, a large steel structure on a reinforced-concrete base. The desert is as flat as a hockey rink in all directions, so the sight of a bridge is a little un­settling. On closer inspection, the creepiness did not fade away: the bridge is wrecked and bent, its once-straight 24-inch I beams warped into long, bowing C‑shapes.