A historic scientific breakthrough that crosses nine borders.

First point in the Struve Geodetic Arc, a 19th century undertaking to measure the Earth's size and shape.

Nicknamed Kazakhstan's Grand Canyon, this natural wonder lies east of Almaty near the Chinese border.

A brilliant turquoise lake in the mountains.

This rare wildlife haven in Singapore feels like you're in the tropical rainforest.

Controversially restored in the 1970s, this giant 15th-century mosque is shrouded in legend.

One of the most ethnically diverse spots on the planet.

Ancient barriers wrap around what was once an important stop along the Silk Road.

Light still pours into the ruins of this ancient Islamic observatory.

Known as one of the most famous parks in Honduras.

This staircase full of Mayan hieroglyphics is perhaps the largest single text in the world.

The largest underground pedestrian tunnel system in the U.S. mostly caters to the people working in the offices above, but provides a great, air-conditioned way to traverse the city.

The world's longest known cave system.

The former home of the Nobel Prize-winning American writer is now home to dozens of six-toed cats.

This small monument marks the divide between the Atlantic and Indian Oceans at the southernmost tip of Africa.

This African beach is home to thousands of rare mainland penguins that are known for their annoying voice.

Nestled in Uganda's Semliki Valley Wildlife Reserve, is a one-of-a-kind safari lodge.

Uganda's smallest savannah park is home to over 350 species of birds and mammals.

Where the White Nile River dramatically cascades between Lake Kyoga and Lake Albert in Uganda.

A gem in the middle of the desert that looks like it came straight from a fairytale.

The largest and best-preserved Roman amphitheater in Africa was designed to seat 35,000 people.

The ancient heart of Tunis is an enormous maze of narrow streets and alleyways.

Founded in 670, this ancient mosque is an architectural time portal.

The largest salt lake in the Sahara is mysteriously alluring.