The mortal remains of an estimated 70,000 people lie in the basement of a monastery in Lima, Peru.

Keshwa chaca, among the last handwoven Incan bridges, crosses Apurimac Canyon in Peru.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

This enormous storm barrier is one of the largest moving structures on Earth, with each arm taller than the Washington Monument.

The Rozenberg wind wall in South Holland makes for smooth sailing through the Calandbrug canal.

Hiding the longest subterranean river known in the world.

The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

Descend into the tunnels to experience the life of a coal miner.

This abandoned Belgian fortress is purposefully being left to nature.

A marble Lucifer hides behind the pulpit of this Gothic cathedral.

Inspired by "The Starry Night" this Dutch bike path turns into a glowing work of art each night.

A visionary precursor to the Internet made of index cards.

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

The world's tallest boat lift stands as a massive piece of industrial tourism.

This collection of solar timekeepers includes the world's first digital sundial.

The vast chamber inside this abandoned cooling tower looks like something out of a sci-fi dystopia.

Invisible bridge parts the waters, invoking biblical images and preserving the ominous feel of an ancient moat.

Ancient man-made caves underneath small town Belgium.

A magical and peaceful ruined Cistercian abbey in what is now southern Belgium.

The "stairway to heaven" lookout tower was built to resist weather, arson, and the laws of physics.

One of the deepest indoor swimming pools in the world.

The Belgian library displays burned books that were salvaged from the fires of both world wars.

This Greek temple, open only an hour a day, was the site of a war of tastes between an architect and an artist.

When you're a great Russian Tsar, even your vomit gets a statue.