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On the sign:
[Emblem of the city of Madrid]
EN ESTE LUGAR ESTUVO DE 1873 A 1929 EL TEATRO APOLO CÁTEDRA DE LA ZARZUELA MADRILEÑA
The theater that led the field of Zarzuela in Madrid (a type of Spanish drama that combines scenes of singing and speaking) was located in this place between 1873-1929. The theater had more than 1000 seats.