The Mob Museum occupies the former federal courthouse and post office in downtown Las Vegas, the building where one of the 1950 Kefauver Committee hearings on organized crime was actually held. That courtroom has been restored and is part of the tour, and it is a large part of why the museum works: the history happened here.
Three floors trace organized crime in America from Prohibition through the Mob's grip on the Las Vegas casinos to modern transnational crime, with real artifacts throughout, including the barber chair Albert Anastasia was killed in and the wall from the St. Valentine's Day Massacre. Law enforcement's side of the story gets equal space, with a crime lab, wiretapping equipment you can operate, and a firearms training simulator.
Admission includes the Underground, a working speakeasy and distillery in the basement. Plan on a couple of hours for the exhibits alone. It is a short walk from the Fremont Street Experience.