A vast Communist-era exhibition space in the Bulgarian capital.

"Holy Wisdom" overlooks the city that became its namesake.

This once-grandiose behemoth of a monument from the socialist era now sits quiet and closed up.

A striking symbol of the Bulgarian capital.

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.

A Bulgarian monument to Russia's role in World War II is constantly being painted in pop culture protest.

This historic black and white monastery is one of Bulgaria's architectural jewels.

This massive concrete sculpture is said to be the heaviest communist monument on Earth.

An abandoned saucer-shaped monument in the Bulgarian mountains.

The largest airborne operation in history was launched to capture this bridge.

This monument pays homage to a classic Dutch tune.

The oldest skyscraper of Europe now stands dwarfed by the surrounding structures.

Rejoice at Amsterdam's ‘pop temple,’ a former church reborn as a raucous music venue.

This large open-air museum showcases the ordinary lives of the people of the Netherlands and pre-industrial crafts and practices.

A bridge that has seen many reiterations over its lifetime.

While most bridges allow roads to pass over water, this one allows water to pass over a road.

This giant radio telescope would be a rusting ruin if it hadn't become such a beloved relic.

These lights mark the area of Rotterdam that was bombed and burned in 1940.

The tallest mountain in mainland Netherlands isn't actually very tall.

The world's largest bicycle shelter can hold more than 12,500 two-wheelers.

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.

The struggle of a small Dutch island against the sea.

A radio telescope for listening to the stars, based in one of the cloudiest countries in the world.

The 20-mile causeway that separates the Netherlands from the sea.