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

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

A striking symbol of the Bulgarian capital.

Sofia's legislative center is continuously reinventing itself.

The Andean town where every single building is decorated with a brightly colored frieze.

The headquarters of one of the world’s longest-running humor magazines bears a noticeable resemblance to a head wearing a Prussian helmet.

The pedestrian traffic signals in Brazil's teeming metropolis light up with clues to nearby landmarks.

The bookstore with bookshelves built into unlikely places.

One of São Paulo's tight urban intersections has become a haven for graffiti artists ever since a single Batman started the trend.

A statue in the center of Dublin dedicated to one of their favorite sons of rock & roll.

One of Ireland's most infamous prisons for rebels including men, women and children.

The 19th-century pharmacy (now a used bookstore) was featured in James Joyce’s "Ulysses," and has changed very little to this day.

Amidst the bustling streets of Dublin, there is a hushed garden that is dedicated to "All those who gave their lives in the cause of Irish Freedom."

The modern birthplace of Irish freedom.

The comedy and tragedy of Oscar Wilde is preserved in a Dublin park, captured in a sculpture of colorful stone.

Some of the saint's blood and bones are said to reside in Dublin.

More than 5,000 artifacts donated by the people of the city, plus a room entirely devoted to the band U2.

The palace window through which Protestant nobles flung two Catholic regents, thus sparking the Thirty Years' War.

The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

The elliptical citadel resisted the advance of the mighty Ottomans several times, thanks to the military prowess of the "Dragon of Albania."

America's original house of worship for Spiritualism, the religious movement based on communing with the dead.

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

A 10 million-ton rock once worshiped by the Tahamies Indians, accessed by an astounding staircase.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.