On December 1, 1913 the Buenos Aires underground, Subte, went into service. 

The Subterráneo de Buenos Aires (Subte), was the 13th subway system  in the world and the first underground in the southern hemisphere. As of 2018, the 64 km metro has 104 stations. serving 1.38 million riders daily. 

in 1909 the Anglo-Argentina tramway company … ” built our first underground line (A), which was inaugurated in 1913 between the squares of Mayo and 11 de Septiembre, and was extended in 1914 to Caballito. The second line (B), built by the Lacroze railway-tram group, was inaugurated in 1930. Finally, in 1933 a third company began the works of a network that would almost double the extension of the previous ones: the Spanish-Argentine Company of Public Works and Finance (CHADOPYF).”

Over 450 pieces of art can be found decorating the platforms all through underground. Subte took the opportunity to display works from 200 artists, turning the subway system into a massive art museum. You can see more of it here Going underground: discover urban art on the Buenos Aires | Official English Website for the City of Buenos Aires. In 1996, Argentina’s post office featured 2 wall tiles from their extensive underground art collection.

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CASA DE MONEDA   Mayólicas-subways of Buenos Aires
Wall tiles from Metro Stations of Buenos Aires 
1996 semi-postal
Designer: A. Mendez