An alleyway plaque is all that remains of the independent Texas' envoy that forgot to pay their rent for over a century.

In this cobwebbed old operating theater, you can practically hear the screams of the unanesthetized patients.

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

The signs of a long buried road can still be found hidden beneath a London sewer grate.

A tongue-in-cheek arcade where the games are based on everyday life.

Hear the quietest sound from across the dome.

A student driver's nightmare.

A vast overgrown cemetery, once known as one of London's "Magnificent Seven."

Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

The curios of pharmacist and collector Henry Wellcome.

One part local history, 99 parts gruesome haunted house.

Banksy gives themself artistic license with this piece of London street art.

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

Repurposed space and ultra-modern construction collide to create this geometric wooden spectacle.

Amsterdam's former hotspot for public executions and dissections.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

A late-medieval Dutch castle with trick fountains in its whimsical water gardens.

One of the great math minds of the 17th century is underfoot in this 900 year old Dutch church.

This stately council chamber hasn't changed since 1545.

Now a museum, this building was once a 14th-century monastery and the place where the founder of the Dutch nation lived and was assassinated.

One of the Leiden's oldest pubs is also the birthplace of the Heineken star.

This small museum collects the Christian remembrances which would otherwise be forgotten.

A lecture hall sink once used by Einstein and other noted physicists is now regarded as a strange science relic.

Elegant marble and old vaults fill this historic Dutch bank turned office space.