Eighty million natural history specimens call this gargantuan museum home.

Large collection from the 3rd millennium BCE.

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

Repository for more than 22 million pickled specimens.

London's old-school healing garden.

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

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

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

Catacombs turned marketplace.

Rebuilt remains of a temple to Roman god Mithras.

The curios of pharmacist and collector Henry Wellcome.

An unusual round church in London with a Templar past.

The quaint little store that is said to have inspired a famous Dickens novel was only given its name after the book was released.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

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

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

These caves secretly held national treasures during World War II.

Legend says this sacred tree was a gift from goddess Athena.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

An ancient octagonal weather station named for the eight Greek gods of wind.

This mystical orb covered in strange symbols is thought to have been used in ancient Greek magical rituals.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.