UNESCO-protected ancient burial ground.

An abandoned saucer-shaped monument in the Bulgarian mountains.

Dine amidst exotic plants at this former royal greenhouse.

This 135-year-old weather station studied the effects of the climate on human health.

Island wonderland for communist autocrats.

Croatia's "hairy stone" fortress is one of the most well preserved Istrian castles.

One of the best-preserved Roman amphitheaters is still used today, but for less brutal events.

Longest fortress system anywhere in Europe.

This picturesque medieval monastery guards a small trove of historic treasures.

Humble beginnings for one of the world's most famous scientists.

Gargoyle head that brings good luck.

The complex has been abandoned since the Croatian War of Independence, barring a stint as a set for 'Game of Thrones.'

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

One of the most photographed locations in the entire city.

An artistic melting pot inside an old roadside inn from the Ottoman era.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

Monasteries on rock pillars, once accessible only by frayed ropes.

An extraordinary house museum and cabinet of curiosities in the heart of Florence.

Drink wine handed out through a window as part of an age-old tradition.

Secret refuge and museum of the Duke of Florence.