Maybe we can't build the world's deepest undersea tunnel in seven years like some cities, but New York still has some serious mega-construction chops. Behold: The latest photos from 120 to 160 feet below Grand Central Station, where workers are building the largest public transportation project in the US.

The East Side Access Project—which Gizmodo explains here—is a 5.6 mile-long project to extend the Long Island Railroad in Queens to Grand Central Station. That means blasting out a gigantic railway not only under the East River, but directly below one of the densest, busiest public transit systems in the world—all without interrupting service.

It's taken the MTA decades (and a veritable machine army) to get this far, but things are starting to come together. When we last checked in with the project, in February, workers were still excavating bedrock from the space below Grand Central. But a recent update on the MTA's Flickr shows the finished concrete walls soaring over the massive tunnels, which now contain actual rails, along with new pipes, lighting, and neatly-finished flooring. With a planned completion date of 2019, there's still a ways to go—but it's pretty remarkable progress.

Meanwhile, not far from the ESA dig site, things are cooking along for the crews at work on the Second Avenue subway line, as well. Check out those new photos from the MTA's Patrick Cashin—along with the ESA images—below. [MTA on Flickr; Gothamist]

The East Side Access megaproject:

Photos: Metropolitan Transportation Authority / Patrick Cashin.

The Second Avenue Subway:

Photos: Metropolitan Transportation Authority / Patrick Cashin.