Vortex-shaped aquarium hosts Europe's largest school of piranhas and other ocean creatures.

The oldest amusement park in the world has been providing a nice spot to have some fun since the 1500s.

A 19th-century subterranean reservoir repurposed as a contemporary art cave.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

Pre-Nazi swastikas adorn the sculpted pachyderms flanking this brewhouse portal.

Danish tourist destination well known for open stalls where vendors sell marijuana on the street.

Beneath Denmark's Højbro bridge, a bronze merman and his seven sons forever mourn for the mother and wife who left them for land.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

Copenhagen's celebrated theme park and gardens.

This abandoned coliseum was intended to be a grand Nazi rallying ground before it was halted at the end of the war.

This lurid German fountain plots the sad course of marriage from dating to death.

The thousands of shades on display — some toxic, others impossibly rare — are a library of more than just color.

A remote candy-striped mountain in the Peruvian Andes straight out of the pages of Dr. Seuss.

This stunning mass of ice spans 121 square miles and is still growing.

Mirrors and glass shards cover every inch of this arrestingly beautiful mosque.

On the Oregon coast there is a natural hole that seems to be draining the sea.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

A swing to dangle you off the very edge.

A solitary tree has grown up all alone on Lake Wānaka, backdropped by the beautiful Southern Alps.

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

The haunting ruins of a military fortress turned astronomical observatory sit on a Sarajevo mountaintop.

Five ancient libraries, little changed for centuries, preserve a medieval archive of Quranic lore and civic documents

The 1936 Summer Olympics site is a crumbling remnant of sportsmanship and a history its host country would like to forget.

A 12th-century fortress containing some of Berlin's oldest buildings.