For the War Room, Ken Adam first designed a two-level set which Kubrick initially liked, only to decide later that it was not what he wanted. Adam next began work on the design that was used in the film, an expressionist set that was compared with "The Cabinet of Dr. Caligari" and Fritz Lang's "Metropolis". It was an enormous concrete room ( long and wide, with a -high ceiling) suggesting a bomb shelter, with a triangular shape (based on Kubrick's idea that this particular shape would prove the most resistant against an explosion). One side of the room was covered with gigantic strategic maps reflecting in a shiny black floor inspired by dance scenes in Fred Astaire films. In the middle of the room there was a large circular table lit from above by a circle of lamps, suggesting a poker table. Kubrick insisted that the table would be covered with green baize (although this could not be seen in the black and white film) to reinforce the actors' impression that they are playing 'a game of poker for the fate of the world.' Kubrick asked Adam to build the set ceiling in concrete to force the director of photography to use only the on-set lights from the circle of lamps. Moreover, each lamp in the circle of lights was carefully placed and tested until Kubrick was happy with the result.