The MTA has posted another incredible set of photos from deep within the bowels of New York City. This latest batch shows the progress of the Second Avenue subway that's being carved 140 feet beneath the bustling metropolis of Manhattan. It's taken decades of planning and years of excavation, but the extension is finally starting to take shape, with concrete walls connecting massive tunnels. But they're still a ways off from completion -- the first trains won't run until 2019.
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