What train goes from Penn Station to Park Ave South?

Take the Uptown E train (of the A-C-E, the blue line) from 34th Street-Penn Station to Lexington Avenue-53rd Street. This station is connected to the 51st Street Station on the 6 train (of the 4-5-6, the dark green line), so you can transfer without exiting the subway system. Transfer to the 6, and take the Downtown 6 to 33rd Street, 28th Street, 23rd Street or 14th Street. All of these stops are on Park Avenue South.