The London Dungeon is ermm, a dungeon in London. Through time the London dungeon has been everything from a leper hospital, An orphanage and a dungeon where people were tortured, A lot of people have died there and a lot of suffering has gone on in the London dungeon so it's no surprise that it should be haunted.
Many people have reported many ghost sightings and strange unexplained happenings in the London dungeon through the years, Everything from ghostly figures walking through walls to sounds of groaning and screaming late at night.
The following video is some security footage from the London dungeon showing a ghostly figure walking down a hall. The ghost footage has two scenes, the ghost appears in the one at the top just after the cleaner leaves. It is quite faint, So look closely and you should see the ghostly transparent figure float it's way down the hall.