A rooftop restaurant hides in plain sight atop Vienna's Palace of Justice.

The beautiful baroque library of the Hapsburg empire.

Dine amidst exotic plants at this former royal greenhouse.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

Along the edge of this fountain are 365 smaller fountains that represent the days of the year.

After 400 years of being closed to the public, this monastery's underground tunnels and secret garden are now a museum.

Hidden in an enchanting ravine, numerous mysterious sandstone grooves hint at ancient pagan rituals.

A historic lighthouse steeped in rumors of ghost and pirate stories.

A millionaire's abandoned swimming pool from the gilded age of one of America's most distinguished families.

Once the center of food production for this small town.

A fire station-turned-church-turned-museum dedicated to the work of seminal light artist Dan Flavin.

This backwater graveyard in the Hamptons became a trendy burial spot and posthumous status symbol for famous artists.

A mysterious air force base built to resemble a Long Island fishing village.

A breathtaking bridge that crosses a vast gorge over a river's torrents, and has a tale of a devil architect attached.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

A stone wall that mysteriously moved three feet from its foundation.

The home of Ireland's last leprechauns is officially protected by the European Union.

These engineering masterpieces are a dominant feature of the Belfast skyline.

A museum marks and documents the site of the Titanic's launch.

One of the largest lenses of its kind ever created, this former ship beacon has been brought down to Earth.

A giant sculpture of the legendary "Salmon of Knowledge" celebrates the return of fish to Belfast's River Lagan.

For part of the year, this innovative greenhouse is painted white to keep the plants from getting scorched.

This former peat factory was transformed into an observatory before being abandoned once again.