Rebuilt remains of a temple to Roman god Mithras.

Hidden beneath the streets of London is a secret subway that only carried mail.

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

In rural Iowa, an imported 19th-century windmill overlooks an unlikely enclave of Danish culture.

Near-constant high winds deform the trees on Spruce Knob, the highest point in West Virginia.

A focal point of in Denver’s skyline for over a century, inspired by a Venetian basilica.

One of the last remaining railway viaducts equipped with a transporter ferry.

This Mexico City subway station will make you feel like you've been transported to the London Underground.

The last intact steam engine factory in the United States.

This massive railroad spike celebrates the 1939 premiere of the movie “Union Pacific.”

The lab where the scientist made his groundbreaking discoveries is preserved on the basement floor of the Faraday Museum.

“It's the quality” (but probably also the drive-through donut tunnel) that has attracted diners since 1968.

This unique bridge curls up like a caterpillar to let boats pass and then unfurls again to span a small canal.

The frozen bubbles that form on the icy surface of this Canadian lake contain enough methane to create a small explosion.

This historic aviation building is now a museum owned and operated by Disney.

The restored ferry is now a dockside museum and a unique bed and breakfast.

One of the few working locomotive roundhouses in the United States.

This mechanical clock performs "Romeo and Juliet" in a Shakespeare-themed New Zealand town.

This multi-level, aqueduct-footbridge hybrid is one of the greatest works of the Spanish Renaissance.

A 2,000-year-old engineering wonder hides beneath an Italian town.

A 250-year-old timepiece-automaton adorned with golden mechanical birds, which still sing to this day.

The skeletal frame of a decommissioned gas-pumping station offers breathtaking views of greater Berlin.

This old medieval prison tower has been a site of astronomical research for more than 250 years.

A historic hotel library in Indiana hides more than a few secrets on its shelves.