Green Park is one of London's Royal Parks. It is just north of Buckingham Palace. There are several references to a "Park" in Virginia Woolf's "Mrs. Dalloway in Bond Street" (1923), however, based on other specific locations, and Mrs. Dalloway's destination of Bond Street, it appears most likely that this "Park" is Green Park.
"And Clarissa, crossing the road, entered the Park, holding herself upright.
June had drawn out every leaf on the trees. The mothers of Westminster with mottled breasts gave suck to their young. Quite respectable girls lay stretched on the grass. An elderly man, stooping very stiffly, picked up a crumpled paper, spread it out flat and flung it away. How horrible!"
"Piccadilly and Arlington Street and the Mall seemed to chafe the very air in the Park and lift its leaves hotly, brilliantly, upon waves of that divine vitality which Clarissa loved."