This half-forgotten fortress was constructed by the Ottoman conqueror of Constantinople.

This former Imperial summer home was the venue for a royal slap that once echoed 'round the world.

Taking the subway here means doing so over a bridge located in the middle of an estuary.

This column celebrates Rome's victory over the Goths, and may be the oldest Roman monument in Istanbul.

Iconic pyramid from famed British architect Norman Foster designed to represent all of the world's religious faiths.

An entertainment center in a huge transparent tent.

A modern tower, symbolizing the legend of a golden egg on top of the tree of life.

Time capsule of a museum, in which the Soviet Union remains alive and kicking.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

The attic of a four-century-old canal house hides a clandestine church.

In 1988, jazz legend Chet Baker fell to his death from a window of this hotel facing Amsterdam Centraal.

One of Amsterdam's narrowest houses is located right across the canal from its widest.

This 22-floor tower's Skydeck offers panoramic views of Amsterdam.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

A floating cat sanctuary on an Amsterdam canal.

Amsterdam's narrowest house facade is a monument to 17th-century tax evasion.

Some 80,000 Delft Blue tiles line the inside of this Amsterdam walkway.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

This ancient Egyptian obelisk still bears the wounds of World War I.

Gutted during the Liverpool Blitz, this architectural husk has been left destroyed in honor of the dead.

This abandoned lock-up was saved because of its connection to a local football team.

Charles Dickens described the concert room in this amazing Victorian hall as "the most perfect room in the world."