When the twin towers fell on Sept. 11, 2001, they came crashing down on the Cortlandt Street subway stop on the No. 1 line. The station was buried under debris, its sturdy beams bent like paper clips. For nearly 17 years, the station has sat unused — achingly missing from the New York City subway map — even as a new sprawling World Trade Center complex has sprouted aboveground. At long last, the station will reopen on Saturday.