In the early 2000s, a huge underground visitor center was built under the Capitol’s east plaza, and one of the eagerly anticipated (though rarely mentioned) features was an upgrade to the garbage collection system. Tens of thousands of legislative staff and millions of tourists pass through the building each year, generating a significant amount of rubbish and necessitating this unique bit of sanitation infrastructure.
The quarter-mile trash tunnel improved the visitor experience in the Capitol while also offering enhanced security screening at a safe distance from the building. (It may have additionally been aimed at placating some fussy members of Congress who are paranoid about people going through their trash.)
Work on the tunnel began quietly in February of 2003 and was completed two years later in time for George W. Bush’s second inauguration. The exact location has never been publicly disclosed, but can be worked out by examining the construction site through Google Earth’s historical imagery viewer. Other than Google Earth’s satellite images, the only other photo of the tunnel is the third image at top, unwittingly published by the Architect of the Capitol and later deleted. All other photos of the Capitol Visitor Center under construction are angled away from the trash tunnel; presumably, that one was an oversight.
Update June 2019: There’s construction going on in Senate Park, but you can still see the tunnel.
Know Before You Go
Lat/Long mark the tunnel entrance on New Jersey Avenue NW.