Last week, the New York Metropolitan Transit Authority updated its Flickr page with stunning new photos showing progress on its subway system's East Side Access project.

The photos give a rarely seen view into what goes into making a subway tunnel.

Take a look:

The MTA's website states that the project burrows 120 feet below the city's streets. To do so uses tunnel boring machines, a process which began in 2009 and was completed in 2011. The caverns being excavated (pictured above) are expected to be complete in 2012.

When finished, the new tunnels will allow the Long Island Rail Road to access Grand Central Terminal for the first time, reducing LIRR traffic into Penn Station.

To see more photos of the tunneling subway project, visit the MTA's Flickr stream here.

(H/T: Gizmodo)