Standing about 100 feet below Grand Central Station, MTA workers are burrowing through solid rock, connecting four out of eight Long Island Railroad tunnels to a central hub.
Officials are projecting September 2016 as the date of completion.
Here is a sneak peak at how far they've come.
A tunnel burrowing east, 90 feet below Grand Central Terminal.
The tunnels will eventually bring the Long Island Rail Road into the west wing of Grand Central Terminal.
This is known as "well way #3" now. But someday it may take people underground from the Madison Concourse.
Ron Cohen has been working on the project for over a year. He is a foreman.
By Federal law, workers must have a tag they flip over from the green side to the red side, when going in the tunnel. There are also tags for visitors as well.
Elevator goes almost 100 feet underground.
Jonathan Medl is the safety inspector. There have been no fatalities, but a few minor injuries.
This sits on a table near the elevator.
One worker says Dunkin Donuts coffee is more popular with the workers.
On the left is a massive cloth tube that pipes in fresh, hot air. It's loud and makes conversation difficult.
This is a massive cavern, 100 feet below Grand Central.
Billy Ury is the explosives expert. He say this is the biggest project he's ever worked on, by far.
This is the tail end of a Roadheader. It has 290 picks, large drill bits, that burrow through the rock.
These are the picks. The Roadheader needs new picks every three or four days.
The Roadheader goes a few feet every day or so.
Bill Ury (left) is the senior inspector and Mark Rhodes (right) is the lead quality engineer.
Ury, and Rhodes take their lunch at Junior's on this day. Most workers bring their own, but occasionally eat at the Grand Central food court, muddy boots and all.