Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

Visit a surreal landscape so otherworldly NASA actually used it to train the Apollo 17 crew.

The chefs at El Diablo use heat generated by an active volcano to cook the food.

This beautifully verdant lagoon is tucked below a massive volcano in a crater atop a black pebble beach.

A completely underwater art museum sends a stark message about humans' impact on the environment.

This record setting conveyor belt system can even be seen from space.

Ancient Phoenician and Roman tombs carved into the rock overlook the Moroccan coastline.

Writers such as Paul Bowles, William Burroughs, and Samuel Beckett frequented this Tangier bookstore.

The first, and perhaps only, monument dedicated to Wikipedia.

This unique medieval artwork featuring the story of the Antichrist remained lost for decades.

An abstract and eyecatching clock/fountain is the centerpiece of this little-known German city.

Europe's official "zero-level," the equator of elevation.

This Greek temple, open only an hour a day, was the site of a war of tastes between an architect and an artist.

The smallest port in France is named after the pirate who created it.

A beautiful lighthouse with as many steps as days in the year, as many windows as weeks, and as many levels as months.

A guitar mounted on a wall in Temple Bar honors the Irish musician.

This neon landmark has been posing this deadpan question to follicly-challenged Dubliners for over 50 years.

At this cozy bar tucked down a hidden Galway backroad, Guinness makes the Gaelic come out.

Originally built to monitor fishing, this Victorian tower now educates visitors about the local salmon industry.

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.