ROSWELL, N.M. — Past the city limits, where the main street with the U.F.O. museum and the McDonald’s in the shape of a flying saucer gives way to a lonely highway coursing through an ocean of scrubby terrain, the green door pops up like a periscope.

Jim Moore, a real estate agent here, sells mostly ranch houses in tidy neighborhoods or stretches of undeveloped land in a place where that is abundant. But for some reason, he said, when an odd listing comes around, it tends to fall to him. And on a recent morning, he pulled off the highway onto a gravel path leading straight to his latest example.

The 25-acre parcel, a 20-mile drive from the city’s downtown, has a worn trailer where the former owner lived and then that green door, which opens on a stairwell heading deep underground. There, visitors who do not fear enclosed spaces will find a marvel of military architecture that has had Mr. Moore’s phone ringing with inquiries from across the country: a missile silo, decommissioned decades ago.

From a real estate perspective, it is a fixer-upper, to put it mildly, one that appeals to a small and idiosyncratic cut of potential buyers (one of whom has already signed a contract, placing it off the market for the moment). At the height of the Cold War, the site had been the home of an Atlas-F missile, an intercontinental ballistic weapon with a warhead over 100 times more powerful than the atomic bomb dropped on Nagasaki in World War II. The missile was taken out of service after just a few years, and left behind was a subterranean lair worthy of a Bond villain, burrowing 10 stories down and capable of withstanding a nuclear blast.