Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.

This foreboding building was the headquarters of the terrifying Spanish Inquisition in Mexico.

The former headquarters of Mexico's Secretariat of Public Education now houses a muralism museum, including Diego Rivera's first large-scale mural project.

A trompe l'oeil mural remembers the original colonial building that once stood here.

To make itself stand out in a city renowned for its numerous museums, this photographic archive resorts to immersively-themed exhibitions.

A disquieting Aztec sculpture displays hundreds of stone skulls representing the victims of human sacrifice.

Iconic red and white plaques show the creative names invented to navigate the city streets.

It would take you approximately an hour and a half to walk to the end of Mexico's largest pier.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.

Rare karst landscape eroded from a flat seabed.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

This crucial gathering spot along the "hippie trail" still displays old notes between traveling beatniks and backpackers.

This fifth-century church is one of the oldest Christian sites in the Balkans.

Step inside this medieval Orthodox gem and travel back to the 16th century.

This solitary monastery may hold the remains of Vlad the Impaler (but probably not).

This elaborately decorated, fairytale-like Romanian royal palace is one of the most striking castles in Europe.

An industrial site turned into Hungary's most cherished natural wonder.

A massive 1830s industrial site once known as Czechia's "Iron Heart" has been transformed into a playground of science, technology, and art.

The only visible reminders of an elaborate engineering project that kept the tower from reaching the tipping point.

Tourists to the mountaintop Sicilian town often overlook its ancient fortifications.

A mysterious ancient elephant said to possess magic powers is now the symbol of a Sicilian city.

A quiet Sicilian village is home to a cafe that had an important role in "The Godfather."