 Embedded in the floor in the centre of the main hall is a replica 25 carat (5 g) diamond, which marks Kilometre Zero for Cuba.The original diamond, said to have belonged to Tsar Nicholas II of Russia and have been sold to the Cuban state by a Turkish merchant, was stolen on 25 March 1946 and mysteriously returned to the President, Ramón Grau San Martín, on 2 June 1946.To either side of the main hall is the "Salón de Pasos Perdidos" ("Hall of Lost Steps"), named for its acoustic properties.