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

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

The smaller of the three towers of San Marino is a former prison inaccessible from the ground level.

This church is named for one of the most dramatic tales in the early Christian church.

Dynastic Home of the De Piro Family.

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

A surprising and unconventional mosque hidden in the subsoil of Istanbul.

These beautiful historic watchtowers were used for both scanning the desert for enemy invaders and observing the celestial world.

This tilted minaret and mosque are a feat of modern engineering.

One of the world’s largest suspended aquariums, located in Dubai Mall.

Iran's "Rose Garden Palace," built during 131 years of rule by Qajar kings, consists of 17 stunning structures.

17th century mosque for Shah Abbas' harem.

This 17th-century structure is a beautiful testimony to traditional Persian architecture

The cathedral stands in New Jufa, Isfahan's Armenian quarter that was established in 1606.

This lake in northwest Iran has started turning from green to red more frequently than scientists are comfortable with.

The largest covered bazaar in the world.

This mysterious but iconic tapered tower appears in many Azeri fairytales and legends.

The building's fluid, wavelike walls are a true feat of architectural ingenuity.

The mastermind behind this palatial hotel perished on the Titanic weeks before its grand opening.

This remote mountain shrine is one of the most sacred Zoroastrian temples remaining in the world.

The tower in this 1,000-year-old mud-brick village seems to vibrate for no apparent reason.

Ancient structures used to make and preserve ice in the deserts of Persia.

Long before air conditioning, Persian architects found an ingenious way to cool off.

The fire inside this temple has burned for more than 1,500 years.