Hundreds of hidden passageways weave through the old quarters of Lyon.

A marvel of Byzantine engineering under the streets of Istanbul.

Roadside collection of 65,000 signs.

Here, at the "world's longest art gallery," you'll find forty miles of ancient petroglyphs and pictographs.

Once the home of a hermetic monk, this cave now houses a small church.

A 20th-century picture show in 3-D.

Where beautiful signs live on forever.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

Malaysian fireflies create a dazzling display as thousands light up in unison.

This former insane asylum now holds a pathological anatomy museum.

Mutant vegetables, transgenic mosquitos, and atomic rodents span the walls of this one-of-a-kind museum.

The largest single concentration of harmless garter snakes in the world is a writhing Canadian serpent orgy.

The world's second largest salt mine, said to have been discovered by Alexander the Great's horse.

The world's second-largest excavated hole.

Abandoned bridge hidden deep in the San Gabriel Mountains.

An isolated dive site teeming with cnidarians.

A geological bull's-eye visible from outer space.

One of the world's most complex timepieces.

Rock-cut caves and 7,000 Buddhist sculptures carved into the nearly sheer face of a sandstone mountain.

A visionary precursor to the Internet made of index cards.

Believed to have once stored either human remains or rice wine, thousands of mysterious stone jars lie in ruin.

One man's artistic vision is a small town government's legal battle.

Ethiopia's "smoking mountain" is in one of the hottest regions on the planet and is home to two lava lakes.

A self-built castle made by a mysterious man.