Green’s Dictionary of Slang

marketplace n.

also market

1. the vagina.

‘Peter Aretine’ Strange Newes 3: Wand. Wh—. I [...] spread my imperfect Limbs [...] claping my hand on my market-place, and saying, here’s your Ware boys, which invitation with a wink, a smile and a chuck under the Chin, brings in the bonny Lads.

2. (US) that area of a city or town where street prostitutes work.

[US]C. Brown Manchild in the Promised Land (1969) 200: When a chick’s habit came down on her, she’d usually end up down in the ‘marketplace’, 125th Street between Third Avenue and St. Nicholas Avenue.
[US](con. 1720s) J. Weeks ‘Inverts, Perverts, and Mary-Annes’ in Journal Homosexuality (1980/81) 6 Fall/Winter 120: The metropolitan subculture of Molly houses, pubs, fields, walks, squares, and lavatories. As early as 1720s, these meeting places had been known as ‘markets’.