A World War II evacuation tunnel turned into a history display of Croatian state and people.

This was the second largest mercury mine in the world and one of the oldest preserved mine complexes in Europe.

This dizzying tower was built to better broadcast the 1980 Moscow Olympics.

This medieval Estonian tower provides access to a series of tunnels that have been home to soldiers, punks, and fine art.

A spectacular Petrine Baroque summer palace commissioned for Catherine I by Peter the Great.

This set of concrete chambers resonates according to different notes of octaves.

One of the oldest lighthouses in the world has been in continuous use since it was first built in 1531.

This stunning limestone waterfall is the highest in Estonia.

Legend says lovers who hold hands while venturing along this stone jetty and kiss at the end will remain together forever.

Rusted cars, trucks, and buses form a fascinating collection of Soviet-era machinery.

Rebuilt several decades ago, its striking murals prevent it from being reconsecrated as a church.

Inside this medieval church resides a unique set of murals.

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

This wall on a street corner in Lower Manhattan has been a blank canvas for a rotation of renowned artists since the 1980s.

Curious crustaceans support an obelisk from ancient Egypt that now stands in modern-day Central Park.

Once thought to be the fabled Holy Grail, it is now known to be an oil lamp.

Oddly shaped rock formation, misassociated with a nearby utopian community.

The home of a formerly enslaved man who went on to become a prospector, entrepreneur, and activist for Black rights.

These natural cliffs look like they are a part of an old castle complex.

Inside this small chapel tucked away in the forest is one of the most well-preserved Danse Macabre frescos.

The Grand Mall in Varna hosts one of the biggest collections of Soviet-era paraphernalia in Bulgaria.

This apartment is a true time capsule of local life in Bulgaria during the Soviet regime.

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

A focal point of in Denver’s skyline for over a century, inspired by a Venetian basilica.