The ruins of an ancient Mayan city, beautifully preserved and only accessible by boat.

A massive underwater sinkhole made famous by Jacques Cousteau.

The remnants of an archaeological camp stand within Tikal National Park.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.

These ruins of a pre-Columbian cliff village are among the most beautiful and well preserved in New Mexico.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

Twenty-seven massive radio antennas on the high plains of New Mexico search for life on other planets.

A 16th-century Andalusian palace.

This underground church is topped with a 500-foot cross that is seen by many as a beacon of fascist hubris.

Abandoned city hidden from the world by tropical forest and isolation on the coast of Kenya.

Just outside of Nairobi lies a large estate surrounded by endangered Rothschild giraffes, who have been fed from the window by Mick Jagger and Walter Cronkite.

One of the oldest and certainly best preserved Cistercian abbeys still in existence.

This pseudo-steampunk weapons facility is the world's largest wood and glue structure, and packs quite a wallop.

The largest hewn stone in history.

The ruined remains of the airport Claus von Stauffenberg departed in his failed attempt to kill Adolf Hitler.

Ruins of a German Castle on top of a towering stone pillar.

A sprawling Baroque park with 300-year-old hydro-pneumatic waterworks.

A magical and peaceful ruined Cistercian abbey in what is now southern Belgium.