The picture on the phone screen is blurry, but unmistakable: At a window, a silhouette materializes out of emerald light, its green, hollow eyes aimed fixedly at the camera. It resembles a specter of some sort.

Or at least, so reasons Mike Harden. In his three years as a guide for the Ghosts of Georgetown tour, he has collected two ghostly images on his cell phone — one captured by a guest two weeks ago at the Halcyon House on Prospect Street NW, the other taken near M Street NW’s famous Old Stone House. He brandishes the photographs as a final flourish on the hour-and-a-half-long expedition, where skeptics are invited to suspend their incredulity during a macabre march through Georgetown’s most eerie haunts.

“I love this tour,” Harden said. “It’s definitely the most fun one that I give.”

Harden said the nightly tours attract thousands of guests, who trace a mile-long route starting at the Old Stone House and ending at the Exorcist Steps. The groups walk past West Georgetown landmarks while Harden discusses the history of the different locations.

Tours operate under the umbrella company Free Tours by Foot. The company has offered D.C. tours since 2007 and has expanded internationally, now including cities such as San Francisco, London and Rome.

For $13, a Ghosts of Georgetown tour participant hears stories about vengeful spirits wreaking havoc in the mansions of unsuspecting families, curses that foretold the untimely demise of an American president every 20 years and ghosts summoned by Georgetown University students through Ouija boards.

One of the stops is outside the Halcyon House, allegedly the most haunted location in the city. Mark Twain’s nephew Albert Clemens inhabited the home in the early 20th century, constantly altering the building with seemingly nonsensical renovations, including staircases to nowhere and doors leading to brick walls. According to Harden, Clemens believed perpetually rebuilding the house extended his own life. Although Clemens died in 1938, Harden said the ghost’s presence is so potent it compelled the founder of the Ghosts of Georgetown tour, Canden Schwantes Arciniega, to refuse to continue as a guide after a supernatural encounter.

Since Clemens’ death, the structure has been sold multiple times, even being used as a university dormitory from 1961 to 1966. Since 2011, the Halycon House has been used as headquarters for S&R Foundation, a nonprofit organization.

“Two years ago, Canden gave the tour to a group of young boys for an 11-year-old’s birthday party, and as she crosses in front of the house, she sees three rope nooses hanging from the fourth-floor window, and as she scans the windows she see a man in a black robe and a wide-brimmed black hat, with a long grey beard and blood- red eyes who lifts a finger to point at her. She screamed and left the boys to fend for themselves, and has declared she’ll never give a tour again,” Harden said.

Visitors often report perceiving otherworldly figures or orbs during the tour, or sensing sudden chills.

One particular ghost — the apparition of former Union General Irvin McDowell — is reported to exclusively bother brunette long-haired young female visitors along the tour. According to legend, his brown-haired lover, Confederate spy Betty Duvall, betrayed him during the Battle of Bull Run.

“As we walked through the tour one night, I was talking to a young girl and I believe I saw a ghostly hand brush her hair to the side and I saw her shiver,” Harden said. “I waited until we crossed the street to tell her what had happened, and I never saw her again.”

Miquita Parker from Laurel, Md., attended the tour to satisfy her curiosity about the supernatural aspects of the District. She said she identifies as a believer in ghosts after two experiences in her childhood.

“When I was three, I remember seeing this figure at my window with all this crazy hair. I woke up crying, and when I called my mom and she said, ‘Oh, that was your grandma,’” Parker said. “I wasn’t scared then because I was so young. … So for me, I definitely believe, which is what made the tour even more interesting.”

Eric Sellers (GRD ’15), who joined Parker on the tour, highlighted it as an opportunity to explore Georgetown from a perspective he had not experienced as a graduate student.

“I enjoyed all the stories, especially about the Civil War,” Sellers said. “I enjoyed the fact that [Harden] knew all these stories about the different areas of Georgetown and the backstories, and instead of just telling us the scary part we also got a history lesson. Because I went to Georgetown, I wanted to find out more information about the stories here.”

Though he said he believes in ghosts since they are mentioned in the Bible, Sellers said ghost tours command popular appeal among believers and skeptics alike because morbid curiosity is inherent in human nature. “I think people go on ghost tours for the same reason that they like going to the theater. They like being scared,” Sellers said. “They look forward to that fear, they want to see if it’s real, they want to satisfy that curiosity. It’s just fear, this weird or creepy feeling that you know something isn’t right. I think that’s what makes it scary, the ambiguity. It’s definitely an adrenaline rush.”

Joshua Han (SFS ’18) said he has seen the tours walking by and sees their appeal, but does not believe in the myths surrounding the Georgetown neighborhood.

“I don’t believe in ghosts, but I think that these ghost tours are pretty interesting,” Han said. “If you walk by the Exorcist steps late at night, you can’t help but feel there’s something spooky about it.”