The Montgomery BART stop, under Market street occupying a space approximately the length of the SW to NE diagonal of the marked box. This, along with Embarcadero and Powell St. Stations is one of the three busiest SF BART Stations and is arguably the most 'downtown' of them. It serves the Daly City, SFO, Pittsburgh/Bay Point, Dublin/Pleasanton, and Richmond lines
Wikipedia article:
http://en.wikipedia.org/wiki/Montgomery_Street_StationCategory:
metro / subway / underground station Address:
Market Street, 598