There is a rambling Addams Family-esque house, long abandoned, that belonged to the Coca-Cola founder’s son. There is a cavernous, two-million-square-foot Sears store, now vacant, that is the largest brick building in the South. And there is a bramble-covered prison farm, damaged in a fire, where Mr. Arend leads a tour through inmates’ cells and the warden’s house.

Image Credit... Troy Eric Griggs

Mr. Arend is a member of Spectre, a group that explores and documents Atlanta’s most post-apocalyptic-looking sites. (The movie “Zombieland” and the television show “The Walking Dead” were both filmed here.)

Membership is free, but you must apply online, promise not to leave graffiti or steal anything, and follow the unofficial urban explorer’s motto: “Take photos. Leave only footprints.” Participants say they have been caught by security guards, the police and even federal officers but have talked their way out of charges.

On a recent outing at an elementary school that has been closed since the mid-1990s, three visitors passed the “No Trespassing” sign without a hint of reverence. “Nobody look at the sign,” one said, “and it doesn’t exist.”

Once inside, they marveled at dusty newspaper clippings still stapled to the bulletin boards, trees growing out of the floor and a gymnasium scoreboard that had crashed to the ground. Then two other flashlights were spotted down a dark hallway. Police? Thieves? Graffiti artists?