U.S. Capitol underground subway and tunnel network

The United States Capitol complex includes an underground subway system and a network of tunnels that link the Capitol to the House and Senate office buildings and to the Capitol Visitor Center. The Capitol subway began operating in the early 20th century and is used primarily by members of Congress and authorized staff, with public access limited to escorted tours. Because these passageways are restricted and largely out of public view, they constitute a concealed layer of the Capitol's infrastructure.