Molly Lester was walking around north Philadelphia a few years ago when she saw a ghost. The specter was haunting the alabaster remains of 1513 North Second Street, a former townhouse. Lester took a picture, the first of what has become a spirited collection of Philly building ghosts—the imprints of demolished rowhouses that linger on their neighboring buildings’ exterior walls. This particular apparition included a white plaster outline where there had once been three floors of rooms, stairs, and built-in closets. As an architectural historian and preservation planner, Lester usually…
