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

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

This park is home to around 500 bird species.

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

The home of half the world's population of critically endangered mountain gorillas.

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

A series of caves within the gorge hold artifacts from the Stone Age.

This stunning waterfall is the backdrop to a site that has seen continuous human habitation for 250,000 years.

A secluded natural oasis hidden deep along a rainforest trail.

The stunningly blue waters of these beautiful caves also have a violent past.

An ice field known for harboring an infamous Martian meteorite turned out to contain the oldest air on Earth.

One of America's oldest Antarctic research bases is abandoned but still just waiting for visiting explorers.

This abandoned Antarctic base sits nearly unchanged since it was forsaken in the 1950s, just waiting for you to visit.

Southern Ocean waters and glacial forces transform the Antarctic ice into these stunning bridges and caves.

At the point of oceanic inaccessibility, you can't get farther from dry land without leaving the planet.

This abandoned Antarctic research station is a Soviet ghost frozen in time.

Russian Orthodox church built on an Antarctic island.

The world's largest neutrino telescope searches for secrets of the universe at the South Pole.

Fire meets ice at the southernmost volcano on Earth.

Natural time capsule containing an alien ecosystem.

Now home to nothing but a weather station and a landing strip, a group of enslaved people were marooned on this tiny island for 15 years.

Scattered ruins and a tiny cemetery are all that remain of a failed attempt to colonize the inhospitable Desolate Islands.

French scientists make up the majority of the few humans to occupy this remote island in the extreme southern Indian Ocean.

This peculiar lake of pitch is so thick and viscous that one can walk on its surface.