A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

Northern Ireland's Brobdingnagian stepping stones.

Ruins of a German Castle on top of a towering stone pillar.

An unusual round church in London with a Templar past.

A Jenga-style cylindrical tower of books that appears to go on forever.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

Each year these high desert hills are absolutely covered with poppy flowers in a surreal show of nature.

This knobby, drooping New Orleans oak is a favorite place both for climbing and for meeting giraffes.

This geothermal hot spring hides beneath a slowly growing mineral dome.

Every autumn, this hillside is ablaze with red summer cypress.

One person's lost luggage is another person's treasure.

The largest self-built castle in the U.S., six decades in the making.

Museum preserving torture methods from the past.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

Rising from the sea like a stone monster.

Once the most densely populated place in the world, this island is now a ghost town.

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

This naturally-sourced hot spring is now home to a clothing-optional resort.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

An Australian lake whose pink hue defies scientific explanation.

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

The very center of Paris is surrounded by a bevy of strange good luck rituals.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.