Stay overnight in the world's most sleekly designed rabbit hole, free of charge.

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

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

This Tuscan lake hides a 13th century town that is still visible when the water recedes.

The largest flower auction house in the world.

A fairytale Gothic castle steeped in Nazi treasure conspiracy theories.

Martin Bricelj Baraga's monolithic sculpture measures the blueness of the sky, and changes color to match it.

This beautifully designed star-shaped fort was the premier defense system of the late 1500s.

A public display of random paleontology.

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

This church, better known for its weeping portrait of the Virgin Mary, also houses the world's oldest existing piece of taxidermy.

Rent out a glass igloo to watch the Northern Lights like you live in the future.

Dr. Strangelove-esque tours reveal the inside a bunker once reserved for Stalin himself.

A top secret Cold War bunker hidden beneath a Latvian spa facility is now open for tours.

This bridge is so steep it looks like a rollercoaster.

A 70-foot-deep ice cave formed by lava from Mt. Fuji on the edge of Japan's "Suicide Forest." 

One of the world's largest tanks mimics the experience of watching rare whale sharks, giant rays, and deep sea creatures from the ocean floor.

"Only the dead get off at Kymlinge."

Swedish skyscraper with a 90° twist.

Huge concrete structures designed as an early warning system for Britain to detect enemy aircraft.

A massive cave complex boasts some of the clearest water (and most charming bats) in the world.

This tri-part waterfall is a little bit of fairytale beauty in the heart of Luxembourg's Little Switzerland.

This Latvian shot factory is still used twice a year to manufacture bullets the old-fashioned way.

An icy lake tucked among jaw-dropping alpine panoramas.