The longest living non-clonal organisms on Earth.

Once thought to be the oldest living tree in the world, Methuselah was germinated before the Egyptian pyramids were built.

At the right time of day, sunlight floods through the roof of this cave and illuminates the small pavilion hidden within.

This ancient cave is home to a museum, bar, and is filled with fluorescent minerals.

These wondrously illuminated caverns extend under the mountains of the Fukushima Prefecture.

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

Perhaps the most spectacular grotto along the Algarve coastline.

Peek into a cave of giant, glimmering crystals.

The ceiling of this cavern is dripping with multicolored marble stalactites.

One of few vertical lava tubes in the world accessible by foot.

This ancient limestone cave system contains many impressive geological features.

The spectacular geological formations make it one of the most impressive caves in Europe.

A subterranean playground in an abandoned slate mine.

Legend has it these caves were created by a deity called Ogba, who is said to live inside the winding subterranean caverns.

Tubing through a cave lit with glowworms is a magical underground experience.

Some 80,000 Delft Blue tiles line the inside of this Amsterdam walkway.

The former home of a mad diplomat is said to still be marked in bloody, arcane scrawls.

This unattributed sculpture in Amsterdam is hiding in plain sight.

This museum housed in a former brothel explores the past and present of sex work in Amsterdam.

This cheese shop also houses a museum devoted to Dutch dairy.

A Portuguese Jewish cemetery filled with stunning grave monuments that date back to 1614.

The attic of a four-century-old canal house hides a clandestine church.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

This 22-floor tower's Skydeck offers panoramic views of Amsterdam.