Built to ward off Napoleon's army, this city-sized abandoned Russian fort is now perfect for urban exploration.

A preserved oak tree about 3,500 years old found in Riga, Latvia.

The widest waterfall in Europe is a natural wonder and one of the only places where fish are caught in the air.

These crumbling Latvian forts make for some haunting seaside ruins.

3,000 market stands in five former Zeppelin hangars.

This collection of solar timekeepers includes the world's first digital sundial.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

Also known as "Robin Hood's tree," this tree became a famed location along Hadrian's Wall before it was cut down in an act of vandalism.

Possibly the oldest of Britain's ancient henges is also one of its most stark.

A red sandstone freestanding monolith rises out of the sea in northern Scotland.

The true age of this ancient stone circle is unknown, but its stunning vista isn't in question.

Amazing and mysterious Neolithic settlement on Scotland's Orkney Islands.

Nestled amid the peaks and lochs of the Scottish Highlands, this inn and pub has played host to outlaws and ghosts.

Overlooking a Scottish loch, this beautifully crumbling castle once inspired a poem by William Wordsworth.

Looking strangely like Rome's Colosseum, this unfinished tower has dominated the skyline for over 100 years.

Now famous as the "Harry Potter bridge," this impressive concrete viaduct has long been an icon in its own right.

A close look reveals that the Scottish monument is just slightly off-kilter.

One man spent 10 years building a spectacular section of road because no one else would.

Islanders once used this dramatic, otherworldly landscape to hide their cattle from Viking raiders.

An ancient Scottish rock formation said to be the gravesite of a giant remains ensconced in legend and intrigue.

The most iconic structure in Scotland has been home to bishops, colonels, and Sean Connery characters.

A castle in the Scottish Highlands has been continuously inhabited since the 1300s.

Where the sleeping monsters of Scotland's oil industry are left to rust.