Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

Macabre astrological automaton clock dating to the late 1400s.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

Ancient ruins hidden underneath a modern luxury hotel.

The studio built by fascists in the hopes of "reviving the film industry" with the occasional propaganda film opportunity thrown in.

A modern sliver of architecture in Roma.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

This World War II bunker now survives as a documentation of the Nazi regime and war crimes.

Once a path for Jewish funeral processions, this unassuming alleyway is rich in local lore.

A memorial in the Tiergarten is a reminder of the suffering inflicted on homosexuals by the Nazi regime.

The last remnants of a massive medieval wall that once encompassed the city of Berlin.

Cold war icon and onetime "hole" in the iron curtain.

One of downtown Berlin's last reminders of its Communist past.

A restaurant and observation deck built in a unique broadcasting antenna.

The walls of Germany's Parliament still show the scars of the Red Army takeover in World War II.

Someone loved this song enough to carve all of its lyrics onto a tree trunk in a Berlin park.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

This museum housed in a former brothel explores the past and present of sex work in Amsterdam.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

What looks like a normal building is really a hollow facade hiding a subway vent.

A mud statue stands in the dark tunnels, seeming to hold up the weight of the city above.

This bridge was constructed from the rubble of the infamous Bastille.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.