A portal into the bricked up canal that runs through the heart of Washington D.C.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

100 years later, they're still down there.

This forgotten boat elevator was an engineering marvel in its heyday.

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

It's possible to walk inside one of the largest Neolithic tombs in Britain.

The largest stone circle in the world has ended up bringing up more questions than it has answered.

This section of the Kennet and Avon Canal has been designated the same level of heritage protection as Stonehenge.

There are hundreds of secret WWII bases hidden in British forests. Built to fight a Nazi invasion, they remained unknown for decades.