Trafalgar Square is the location of the scene in the first painting Mary sees of Perry's, Two Sisters, when she is critiquing art at the Society of United Artists. It is a public square in the City of Wesminster, Central London, established in the early 19th century around the area formerly known as Charing Cross. 

Trafalgar Square, London 2 - Jun 2009.jpg

https://en.wikipedia.org/wiki/Trafalgar_Square 





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