Spoiler
A conversation pit is an architectural feature that incorporates built-in seating into a depressed section of flooring within a larger room.
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The conversation pit was popular from the 1950s to the 1970s, seen across Europe as well as North America. Modernist architects Eero Saarinen and Alexander Girard used a conversation pit as the centerpiece of the influential Miller House (1958) in Columbus, Indiana, one of the earliest widely publicized applications of the concept. A red conversation pit (since covered, but recently restored) was later incorporated by Saarinen into the 1962 TWA Flight Center at John F. Kennedy International Airport in New York.
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I was a boy in the 70s. I wish I had been older. I would have died to do that if I got the chance.