Chicago has had its share of killers, but perhaps none more haunting than H.H. Holmes, the pharmacist who turned a hotel into a torture castle. Ahead of the 1893 world’s fair, Holmes moved to Chicago and started outfitting a three-story hotel with all manner of nefarious contraptions, including gas lines, secret passages and trapdoors, hallways to dead ends, chutes to the basement, soundproofed padding, and torture devices strewn throughout a maze. The gas allowed Holmes to knock out his guests before the worst of what was to happen came next, often on his surgical tables. He then burned the bodies in the building’s furnace, selling skeletons to medical schools and running life insurance scams. In all, he copped to more than 30 murders—found only after a fellow scammer turned him in for falling short on a financial agreement—before he was hanged in 1896.