This spire on an Austrian mountain is wrapped around a long spiral slide and has the world's tallest wooden observation deck.

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

This Big Sur waterfall drops 80 feet directly into the Pacific Ocean, and inspired the hillside house up top.

This iconic 1,000-year-old medieval castle is a favorite of the film industry, most notably as the location for Hogwarts in Harry Potter.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

A well-preserved medieval village nested on a rocky outcrop and surrounded by a network of cliffs, natural bridges and canyons.

Once an indicator of social class, the color blue has come to define this city on the edge of the Thar Desert.

An architect's childhood fantasy treehouse made real.

Creek water that starts here has a 50/50 chance of ending up in the Atlantic or the Pacific.

A submerged archeological park still holds the wonders of a Roman Sodom.

A remote forest of stone pillars along the Lena river.

Bioluminescent firefly squid light up this Japanese fishing port.

Stay in your own little bubble.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

An underwater restaurant, surrounded by a coral reef.

Mysterious rocks that ring musically when struck.

One of the world's largest model railroads is a mind-boggling achievement.

A subterranean playground in an abandoned slate mine.

One of the largest ochre quarries in the world, hidden in a limestone landscape.

Réunion Island's highest point is a 2 million-year-old volcano and a paraglider's paradise.

A public park off the beaten path with a beautiful waterfall and 13th century Cistercian abbey.

This imposing tower named after the mythical sword of King Arthur is considered the tallest freestanding climbing wall in the world.

Tubing through a cave lit with glowworms is a magical underground experience.

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.