The National Theatre (Washington, D.C.)
“For almost a century the National has been haunted by the friendly ghost of actor John McCullough, reputedly shot and killed by a fellow performer. The two men argued while washing clothes in the Tiber Creek, which then flowed through the basement backstage. A rusty pistol, perhaps the murder weapon, was unearthed under the stage in 1982, near where McCullough’s remains are rumored to lie in the earth beneath the stage. According to legend, his spirit roams the theatre on the eve of opening nights, and was once seated in the audience.” (Thanks to Myponine for the suggestion.)