Through the Keyhole was a gameshow hosted by Sir David Frost in which celebrity contestants would have to guess which other celebrity's house was being explored by Lloyd Grossman and his camera crew. The contestants would sit in the studio and watch a short film of the inside of someone's house and would then discuss amongst themsleves whose house they thought it could be.
Various clues were given during the film with the cameraman lingering on a sporting trophy or a particular book title on the coffee table for example and the eagle-eyed contestants would have to try and pick out other clues from the interior of the house.
Through the Keyhole was not only the title of the show but was also part of Sir David Frost's catchphrase: "Who lives in a house like this? We'll find out as we go Through the Keyhole."