This crumbling Portuguese ruin overlooks the populace it once ruled.

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

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Scattered throughout London are ancient remnants of the city's former bounding wall.

A cluttered and astounding collection of antiquities and curiosities.

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

The final resting place to 300 Victorian-era pets hides inside the city park.

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

A historic house left in "dramatic still life."

Rebuilt remains of a temple to Roman god Mithras.

Several plaster noses are hidden in plain sight around London's Soho neighborhood.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

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

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The Swedish flag over this small naval fort signals that the nation is at peace.

Stockholm's tiniest statue is of a small boy looking at the Moon.

Stockholm's narrowest alley is barely over two feet wide.

Now a hotel, this former bank was the site of a robbery that spawned a psychological phenomenon.

The library's graceful rotunda is like a bibliophile's temple.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

Two distorted Romanesque columns hold aloft a mine cart in honor of laborers who died during WWII.

A 11-foot former president stands on a Kosovo street that also bears his name.

A futuristic, brutalist masterpiece that is also strangely prison-like.

The elliptical citadel resisted the advance of the mighty Ottomans several times, thanks to the military prowess of the "Dragon of Albania."