These abandoned Cold War-era bunkers are now a designated refuge for endangered bat species.

A brush maker used his factory to protect blind Jews from the Gestapo.

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

A fascinating insight into daily life in the Eastern Bloc.

A 12th-century fortress containing some of Berlin's oldest buildings.

A narrow passage next to a cafe leads to a courtyard exploding with murals, tags, and paste-ups.

The abandoned remains of this Victorian brewery hide crumbling bowling alleys and rusting industrial gear.

The most visited, and possibly most controversial, museum in Germany.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

Breathtaking and huge 430 year old maps of Italy.

The final resting place of the poets Shelley and Keats.

Ancient ruins hidden underneath a modern luxury hotel.

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

Rome’s legendary peephole vista is also a former Crusader stronghold.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

This hill made entirely of ancient Roman jars was simply a garbage dump to the people of the time.

An 18th-century post box used to alert the church of sick and ailing foreign pilgrims.

Plaques on its facade commemorate the Tiber's most destructive deluges.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

A statue representing a lost Roman profession that was vandalized for centuries.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.