2124 Fairmount Ave., 215/236-5111,
The place is creepy enough on a regular tour, but every October, the former prison hosts Philadelphia’s  most frightening tradition. Terror Behind the Walls is Eastern State Penitentiary’s  haunted-house tour, where guests walk through long, shadowy corridors and past dark, seemingly empty cells.
Enhanced by realistic cosmetics and incredible acting, deformed and decaying monsters are everywhere and eager to greet you. Tours begin at 7 p.m. every night and continue every 30 minutes.
Be warned: There is often a line around the block to get into this popular event. Ask about the more subdued “Family Night,” which offers a somewhat less terrifying alternative for the easily frightened and younger crowds.