This Soviet-era "closed town" was a top secret uranium producer often left off of maps.

The ruins of an Estonian prison are drowning in the quarry lake where the convicts were once forced to work.

The Guardian of Tallinn.

Latvia's symbolic mountain-shaped national library is home to millions of cultural tomes.

The most elaborate of 12 medieval arched doorways to the old city of Burgos.

Two large posteriors in one giant statue.

A hidden three-foot-wide house separates these two regal churches.

The stunning interior of this Gothic church is covered in ornate gold details.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

Originally used to sell brandy, the bull-shaped billboard became an iconic symbol of Spain.

An exquisite collection of fairytale conveyances that puts most car museums to shame.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

"Portugal's Stonehenge" is made up of nut-like stones aligned with the heavens.

The world's oldest bookshop still in operation.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

Giant topiary dog once played a role in a terrorist bomb plot.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

A 300-ship graveyard, with a few still visible at low tide.

Every summer, an open-air swimming pool appears at the base of a Finnish city's beloved winter attraction.

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

The geographical center of Budapest is marked with a 10-foot-tall stylized zero.