An important landmark in the history of algebraic logic.

Started nearly 100 years ago, this science experiment just keeps on going, ever so slowly.

An early Portuguese serial killer's head is alarmingly well preserved in a jar at the University of Lisbon.

Hidden treasures belonging to Mongolia's most revered and multi-talented monk spent decades buried in the Gobi desert.

Rock-cut chamber at top of an outcroup, reached by a mountain stairway of forty steps.

Thanks to its heroic service during WWII this Soviet castle has been turned into a monument towered over by a brutalist titan.

Where the Great Wall of China meets the sea.

An abandoned underground bathroom is now a space for public art.

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.

The top of society once luxuriated in this world-class hotel, which continues to impress, even in ruin.

A huge maze complex and whimsical miniature village in Tasmania.

The world's longest and deepest train tunnel.

A climbing route in the mountains of Italy’s Dolomites, built for soldiers during World War I.

Colin Stokes "got a bit carried away" and built a castle that looks like something out of Tolkien.

This painted Lego bridge is the product of over a century of locomotive history.

The bust of Romania’s most notorious ruler, Vlad Dracula aka "Vlad the Impaler," keeps watch over the ruins of his medieval court.

One of the world's tallest waterfalls wasn't revealed to the world at large until 2006.

Of the many chalices in the running for the Holy Grail, this one in Valencia Cathedral sure looks the part.

This unique bridge physically lifts a piece of the road into the air to let boats pass by.

This mummified mermaid corpse is an aquatic curio that was eventually revealed to be a fake.

A boulder carved into the shape of the cosmonaut's head.

The medieval castle built as headquarters for the Pope's secretive Knights Templar.

The great Danube river starts here.

One of the most breathtaking railways in Europe also takes one of the steepest climbs, from fjord to mountain plateau.