The lowest point in South Dakota and the source of the Minnesota River.

17,400 lbs., 12 feet in diameter, and 29 years in the making.

A rare set of strings by famed instrument maker Antonio Stradivarius is on display in the Royal Palace.

For decades, Puerta del Sol has been illuminated by a giant, guitar-wielding bottle of sherry.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

Commonly acknowledged as the only public monument to the Devil himself.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

A lush indoor jungle fills this bustling Madrid transportation hub.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

Italian cave with exceptional acoustics and an unsavory history.

Museum celebrating the ocean, with the largest wunderkammer dedicated to sea exploration.

This massive blockhead sculpture hides an entire library.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.

These caves secretly held national treasures during World War II.

Legend says this sacred tree was a gift from goddess Athena.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

An ancient octagonal weather station named for the eight Greek gods of wind.

One of Antoni Gaudí’s earliest buildings, built between 1886 and 1890 for the industrialist Eusebi Güell.

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

An early 20th-century bullring converted into a modern shopping center.

The oldest giants in Catalonia are now displayed in a 14th-century Gothic church.