You can see three Irish counties from this Neolithic hillside fort, once the seat of the Kingdom of Ailech.

Mortarless walls that stretch for miles are a lovely solution for creating grazing land in the harsh terrain of the Aran Islands.

The world's largest reflecting pool is just two centimeters deep.

This salt marsh in Southern France is as pink as the flamingos that inhabit it.

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.

This French castle is said to have once held the Holy Grail but is now a gorgeous mountaintop ruin.

This off-limits room in the National Library of France is home to a system of pneumatic tubes, once used to bring books to readers.

A modern-day Lascaux cave underneath Paris.

The largest coin pyramid in the world is a carefully balanced stack of over 1,000,000 pieces.

Things aren't quite what they seem at this mind-bending museum.

A narrow strip of land is home to the tallest migrating dunes in Europe.

Museum deep in the catacombs of St. Michael the Archangel Church is explored by touch, sound, and smell.

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

Spend the night in 1920s Latvia in this historic recreation and movie set.

A former Latvian headquarters of the brutal KGB secret police is now open as a grim reminder of their atrocities.

This abandoned secret city is a crumbling wonderland of Soviet ruins.

Go inside to really appreciate this 500-year-old technological masterpiece.

Architectural monsters are devouring this palace's every door and window.

A collection of objects supposedly singed by the hands of souls in purgatory.

An Italian hillside ghost town.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

Just another ancient, mysterious Irish stone circle.

The remains of this deep, dark mine have left behind a haunting rocky warren of tunnels.

Petrified footprints of one of the very first vertebrates to walk on land.