This amazing ancient cave was kept secret for seven years to protect it from the public.

These numerous Israeli caves were dug out over hundreds years for reasons ranging from hideouts to burial sites.

You can row a boat through this ancient underground reservoir.

This off-beat, quirky communism-themed bar isn't afraid to poke fun at its history.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

The massive white mound and accompanying water terraces are a striking geological oddity.

Tucked away near more famous landmarks lies a statue meant to symbolize the confluence and continuing development of human culture.

A series of caves under Castle Hill that once held the prisoner Vlad Tepes, better known as Count Dracula.

A statue in Budapest's Liberty Square honors the former U.S. president's efforts to end the Cold War.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

This Hungarian stilt village is built in a lake that never freezes over due to the power plant that that uses it as a cooling pond.

Martin Bricelj Baraga's monolithic sculpture measures the blueness of the sky, and changes color to match it.

One of the largest barracks of the Austro-Hungarian monarchy's military is now an abandoned ruin.

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

A castle-like sea fort from the 17th century is now a museum to oyster farming.

Abandoned medieval hill town.

The mental institution where Van Gogh created some of his most famous work now allows guests to walk in the artist's footsteps.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

A tiled, multi-level garden of survival in Lyon.

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

World's largest permanent maze made of 18,000 conifers.

Large Hadron Collider and the Birthplace of World Wide Web.