Not merely a museum – but a whirring powerhouse that offers a subterranean peek into the heart and soul of cable car operations.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

Visible below the waves are memorials to the city's Gold Rush dead.

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

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A gigantic, symbolic artwork covers the side of the building.

Once home to an aristocratic family and a workers' organization, this intricately tiled building now houses a chain restaurant.

These spectacular, symbolic serpents lie within the shadow of the Great Temple.

This incredible college library is a visual masterpiece of mosaic art. It also looks kind of like a giant boombox.

A disquieting Aztec sculpture displays hundreds of stone skulls representing the victims of human sacrifice.

A museum in the former home of Marxist revolutionary Leon Trotsky.

The famous artist couple lived and worked here, in two different houses separated by a bridge.

Frida Kahlo's childhood home, now a museum of her life and works.

From Tintin to the Smurfs, Europe's greatest graphic icons are celebrated in a grand Art Noveau gallery.

Climb inside an iron crystal magnified 165 billion times its normal size.

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

This ghost town in Belgium will lose its street art when it ceases to exist.

A little sculpture with a large wardrobe.

A 14th-century fortified keep showcases the masterpieces of an ingenious 20th-century clockmaker.

Most prolific publishing house in the 1600s open to the public.

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

This sprawling Belgian fort was once thought of as impenetrable but now it is simply an abandoned relic.

The patron of this extravagant Art Nouveau confection insisted that nothing less than a boat should project from its facade.