Inside the corridors of this flea market, visitors are sure to find some obscure and odd treasures.

An ornate private entrance to the Vienna subway built specifically for the emperor.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

Collection dedicated to funeral rites, equipment, and mourning rituals of the Viennese.

This Austrian museum celebrates the work of famous forgers and their inimitable imitations.

The beautiful baroque library of the Hapsburg empire.

Op-art architecture designed for happiness.

The former private quarters and office of Dr. Sigmund Freud now hosts a museum housing the works of the founding father of psychoanalysis.

A new sculpture calls attention to climate change in the centuries-old city it threatens.

Thousand-year-old Viking runes adorn an ancient Greek lion at the entrance to the Venetian Arsenal.

Those who own or stay at this 500-year-old, allegedly cursed house often meet terrible fates.

100 year tradition of fist fights, marked by marble footsteps.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

Venice's "Island of the Mad."

This fairy-tale castle would make Dracula (who is said to have been imprisoned there) jealous.

Once the legendary capital of the Dacian Kingdom, this city has been reduced to mere ruins.

Known as the Hintz House, this medieval pharmacy has been an apothecary's haven for nearly 450 years.

The romantic botanic tunnel feels like a well-kept secret.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

This cafe offers a curated collection of treats and tipples made by monks and nuns.

A temple to modernity, tucked away amid Barcelona's more well known museums.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.