A vast and unlikely aviation museum kept alive for over 50 years due to one man's tenacity.

This impressively complicated radioastronomy research center was once a tool of Soviet spies.

This charming Latvian lane doubled as Baker Street on the Soviet Union’s version of Sherlock Holmes.

Built to ward off Napoleon's army, this city-sized abandoned Russian fort is now perfect for urban exploration.

The reconstruction of this prominent building fulfilled a long-written command.

A top secret Cold War bunker hidden beneath a Latvian spa facility is now open for tours.

This Estonian watchtower looks like a big tree with two giant bird nests on it, complete with a "golden egg."

This abandoned fighter jet launch center is now a haunting street racing course.

Abandoned Soviet base once stocked with short and medium range missiles pointed at western Europe.

This soviet pilot's graveyard is filled with headstones made of airplane fins.

The secret cells in the basement of the KGB's Estonian "Grey House" have been preserved as a grim Cold War museum.

Once standing on solid ground, this slender beacon is a victim of the very shoreline it was charged with announcing.

A decommissioned submarine base makes a great space for graffiti art.

Rusted cars, trucks, and buses form a fascinating collection of Soviet-era machinery.

The gutted remains of this Estonian mansion are a monument to a tragic love.

Disused seaplane hangar gets a second life as the jaw-dropping home of Estonia's museum of maritime history.

An empty relic of the Moscow Olympics crumbles away in Estonia's capital.

The ruins of an Estonian prison are drowning in the quarry lake where the convicts were once forced to work.

Two standing giants remain as a tribute to Luxembourg's metallurgical past.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

Once the local rulers had gone these enchanting ruins housed common folk in an almost real life fairy tale.

Ruins of a late 1950s Polish ski jump ramp in the middle of the city.

This lakeside bunker complex in Mamerki, Poland, housed the Supreme Military Command of Nazi Germany during World War II.

An impressive monument to Poland's independence.