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

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

Quite simply the largest tree in the world (by volume).

Hear the quietest sound from across the dome.

It houses the remains of a 17th-century version of the Titanic.

Hollywood's most famous landmark, the "temporary" sign that has stood for decades longer than intended.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

Elevated freight railway turned wildly successful urban park.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

Not quite the cultural gateway between China and Sweden its designer imagined.

Stone carvings record the Norse myth of Sigurd, providing a glimpse into Scandinavia's transition from paganism to Christianity.

The scars of a remarkably organized public protest to save 13 elm trees are still visible in this Stockholm park.

A golden plaque marks the site of the mysterious unsolved assassination of the former Swedish prime minister.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.