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

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

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

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

This once-derelict building is now one of the most beautiful bookstores in the world.

Something's watching you.

A fire once nearly devoured this gorgeous 14th-century Gothic cathedral.

This snug medieval lane is one of the narrowest streets in the world.

The European towns of Brașov and Râșnov each have proud signs reminiscent of the Hollywood sign.

This hauntingly beautiful cemetery outside a medieval citadel is full of winding paths and ivy-covered graves.

Nine centuries-old fortresses guard the walls of this medieval Romanian city.

The famed literary character has a unique connection to this city.

These bronze sculptures sow whimsy by hamming it up on a pedestrian mall.

This memorial commemorating fallen Swiss Guards of the French Revolution has been called the saddest stone in the world.

The largest collection of Indigenous Australian artifacts in the world, and the rare museum where wood-and-glass cabinets have trumped interactive exhibits.