A curiously placed cannon along a roundabout in Freetown marks the boundary of the old city.

Tens of thousands of Africans rescued from slave ships passed through this gate before being settled in Sierra Leone.

On an idyllic island off the coast of Sierra Leone, remnants of the defense of the slave trade and its later abolition.

A seaside cemetery honors the Commonwealth soldiers and sailors that died in Sierra Leone during World War I and II.

A centuries-old house, once part of the wall of Granada, sports musket barrels from the battlements which allude to its original owner.

A museum dedicated to the centuries-old cave dwellings that housed marginalized communities on the outskirts of the former capital of Muslim Spain.

The propeller from the first steamship launched on Lake Tanganyika.

The "Key of Keys" for Washington, D.C. and the apocryphal landing place for the military campaign that started George Washington's career is now at the bottom of a well.

A hill outside of Kasempa is the location of a famous battle between the Kaonde and Lozi tribes.

This statue honors a pillar of the early New Haven Black community.

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

It's not quite as old as its Roman appearance suggests, but this piece of infrastructure served Guatemala City for centuries.

A Zulu warrior is buried far from home, near the very northern border of Zambia.

The first Catholic Mission to the Bemba people of Zambia still stands.

Once a meeting point for Swahili slave traders, this ancient tree is now a monument to those killed by the slave trade.

This old brick building has held everyone from prisoners of war to freedom fighters during its turbulent history.

A small cemetery on a hill overlooking Mbala contains the history of the town's colonial past.

Rare pigmented engravings cover the walls of this Stone Age shelter.

A memorial marks the spot where a plane crash killed several United Nations members on a peace mission to the Democratic Republic of the Congo.

The ruins of a massive World War I fort overlook the border between Zambia and Tanzania.

Africa's fourth longest river originates from a burbling spring in a secluded stretch of woods.

The abandoned tower is the last remnant of Lusaka's first major power plant.

This fascinating cave is packed with prehistoric rock art and Stone Age tools.

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