Even France's favorite aquatic son Jacques Cousteau, couldn't get to the bottom of it.

Ancient pueblos built into the base of a natural canyon wall.

A small island dotted with old, historic Finnish buildings.

An abstract monument to a symphonic composer.

This irregularly shaped sea fortress has defended not one but three different sovereign states.

A subterranean house of worship carved right out of the bedrock.

The reconstruction of this prominent building fulfilled a long-written command.

A black cat protests the City Guild in Riga's Old Town.

The oldest housing complex in Riga is a mini timeline of architectural trends.

Flamboyant architecture from the turn of 20th century.

3,000 market stands in five former Zeppelin hangars.

Inside this medieval church resides a unique set of murals.

For the last century, this international border within a small town has appeared and disappeared various times.

The oldest continuously operating pharmacy in Europe.

Estonia's largest creative city is a vibrant bohemian hub located within a former industrial complex.

Man-made mineral caves house massive bat colony.

Disused seaplane hangar gets a second life as the jaw-dropping home of Estonia's museum of maritime history.

An empty relic of the Moscow Olympics crumbles away in Estonia's capital.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

A slice of central Asia in the middle of Berlin.

The largest Canadian war cemetery in Italy commemorates those who died in one of the bloodiest battles of the Italian campaign during World War II.

A massive marble foot is tucked away in a small alley near the Pantheon.

The only visible remains of this ancient Greek underground temple is its roof protruding from the earth.

The Adriatic's most famous wind can be reliably experienced in the city's Marina.