The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

The most visited, and possibly most controversial, museum in Germany.

One time home to turn of the century explosives, now hidden under the Bay Bridge.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

Staircase winds down the side of Telegraph Hill through gardens, wild parrots flying overhead.

After starting as a whimsical tourist attraction that eventually found its way to ruin, these renovated canals offer a lush and exotic locale on the Pacific Coast.

Physicist’s epitaph provides final confirmation to a career of turmoil.

On a winding Vienna side street, one museum has turned their windows into a monument to history’s peace-minded heroes.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

Museum devoted to the artificial language of Esperanto.

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

Apartment complexes built into huge repurposed natural gas tanks.

The Habsburgs' royal collections of art and wonders.

The townhouse where the "Blood Countess" Elizabeth Báthory started her murderous career.

Dine amidst exotic plants at this former royal greenhouse.

A silly medieval mural preserved on the side of a Viennese house.

Beautiful Austrian natural history museum with carved ceilings and row after row of ancient taxidermy.

Legends surround an ancient tree trunk riddled with nails for good luck.

Baroque celebration of the end of the Great Plague of Vienna.

Op-art architecture designed for happiness.

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

One of the most unusual geological features, recognizable from a dozen hit movies.