An unwanted roommate, the ghost who was invited in.

The building dates to the late 1800s. Perched on an outcropping of granite in upper Manhattan, it often invites comments with its shared double staircases. The top floor is effectively a five-floor walk-up, and visitors often compare the descent to mountain climbing.

Rumor has it the buildings were originally single families built for four sisters. A local merchant told me he…