An icy lake tucked among jaw-dropping alpine panoramas.

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.

Ancient paintings known as the "Sistine Chapel of Cave Art."

This structure atop a craggy cliff in one of the most beautiful parks in Paris boasts an unbeatable view.

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

Medieval irrigation channels built into the sides of mountains provided Valais with water for hundreds of years.

The idyllic island where the philosopher Jean-Jacques Rousseau spent “the happiest time of his life.”

One of a series of no-purpose kinetic artworks by Swiss sculptor Jean Tinguely.

This little Greek plateau is home to thousands of rustic, white-sailed windmills.

Every spring, locals see the shadowy figures of a ghost army of slain Greek soldiers descend upon this ruined fort.

The abandoned summer estate of the former Greek Royal Family.

Overlooking the harbor is a beautiful neglected mansion guarded by two Egyptian sphinxes.

Gladiators once walked this ancient, subterranean passage.

This seaside sanctuary was once one of the most important religious sites for women in ancient Greece.

Swiss vineyards in a UNESCO heritage site.

Over 3km of caverns and caves at the Switzerland-France border contain the largest underground river in Central Europe.

Traversing steep Alpine slopes, this engineering marvel is one of the longest and highest funiculars in the world.

For centuries no one knew there were hundreds of bones and precious artwork hidden beneath this Swiss church.

A cablecar-station-turned-revolving restaurant with 360-degree views of the Swiss skyline.

This historic covered bridge contains a series of macabre paintings that communicate one thing: everyone dies.

This small museum once served as a royal hunting pavilion for King Otto Friedrich Ludwig.

A man's head is enshrined beneath a statue near the first building constructed for the modern Olympic Games.

This open air archeological site houses almost as much wildlife as it does classical religious artifacts.

The ghost town where the villagers refuse to leave.