This hidden green space is the city's second largest conservatory.

A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

London's smallest police station is barely the size of a phone booth.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

This 1920s Dutch barge is now a floating bookstore.

Catacombs turned marketplace.

Rebuilt remains of a temple to Roman god Mithras.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

This churchyard arbor is surrounded by hundreds of gravestones placed there by author Thomas Hardy.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Lyon's "Wall of the Silk Weavers" is one of the largest murals in Europe.

At this archaeological site, visitors can explore the ruins of the capital of the former Roman province of Moesia.

Sealing couples' love since just after World War I.

Curious carved stones and bird-like wings are a symbol of Serbian resilience and freedom on the site of a WWII massacre.

Serbia's master of striking memorials erected a forgotten, hidden gem in the hills outside a tiny village.

One of Belgrade's most beloved animals.

The ruins of a military-industrial complex now host concerts and more.

This outcropping was once home to a medieval monastery destroyed during the Ottoman conquest.

Legends of treasure and spirits flow from this this fairy tale-like oasis.

Backwards hour and minute hands and a timing mechanism that fluctuates with the temperature led to this clock tower's local nickname.

A Stockholm metro station is home to an escalator that is not only the longest in Sweden, but among the longest in the world.

From a distance, this structure looks like an ordinary office building but a closer inspection reveals a unique facade.