US Congress members have a private subway system that runs beneath the Capitol.

The subway connects congressional office buildings with the Capitol building.

The government shutdown may still be underway, but one system used daily by lawmakers is still running.

Beneath the US Capitol in Washington, DC, a system of tunnels connects the Senate and House floors with various office buildings where senators and representatives spend their work days.

At the heart of this tunnel system is the Capitol subway, a private three-line subway system that transports legislators on two-minute journeys from their office buildings to the Capitol.

The subway system dates back to the construction of the Senate office buildings in the early 1900s.

These days, subway cars run between locations hundreds of times a day, and have even functioned during past shutdowns. Photos from the current shutdown, which started October 1, show senators aboard its cars and speaking with journalists in its hallways.

Look inside the little-known rail system that has moved Congress members for over a hundred years.

Senators began using cars to move beneath the Capitol in 1909.

Senators began using cars on the underground tunnels to commute from their office buildings to the US Capitol as soon as the offices were built.