https://wearechange.org/theres-hidden-network-tunnels-underneath-washington-dc/
It is well known that Freemasons certainly played a role in the construction of Washington D.C., and the city is full of persisent rumors that the street layout and other buildings are embedded with masonic code. It isn’t surprising that networks of underground tunnels (and even a subway just for those on Capitol Hill) were built beneath the city. More unique than the existence of the tunnels is how they’ve been hidden and if and how they are being used. In Washington D.C., they’re like underground cities, with all the things you would need from the outside world, moved underground. Streets become hallways lined by rows of earth and lights.
All of the buildings in the United States Capitol Complex are connected by tunnels and underground walkways, which provide easy passage between legislative office buildings, the Capitol, the Capitol Visitor Center, and the Library of Congress, used in inclement weather. The tunnels connecting office buildings are open to the public, but those connecting to the Capitol require security clearance. Small electric tramways run from the Capitol building to the Russell, Dirksen, and Hart Senate Office Buildings and to the Rayburn House Office Building. The tunnel between the Capitol and the Cannon House Office Building displays winning pieces of artwork from the annual Congressional Art Competition for high school students.