Iglesia de San Manuel y San Benito
Time Out says
Located in C/Alcalá, in front of El Retiro park, this church is one that the people of Madrid may not know well but should. The work of architect Fernando Arbós y Tremanti, it's one of the best examples of neo-Byzantine architecture in the city. Inside the small church are the burial plots of Catalan businessman Manuel Caviggioli and his wife Benita Maurici, who donated the land for the construction of the temple. Its most impressive feature is its large dome in shades of green, blue and gold.