- This is a dead cell. No food, no water, until you die. There wasn't any light.

NARRATOR: The cruelty of the slave trade didn't begin when displaced Africans stepped onto plantations, nor when they began their journey across the Middle Passage. It started here.

- About 150 women were here, and at that time there were no toilet facilities for them. And this is the original floor.

NARRATOR: On the coast of southern Ghana sits one of the oldest slave castles in the world. Millions of Africans were held here for three months at a time, before being shipped across the world in chains.

- Initially, the trade was butter. When they shifted to slavery, the same rooms were also converted into dungeons.

MAN: One of the things you can kind of tell, as soon as you get in this room, is the smell. The fact that you can still smell menstruation, because of its original floor, I guess it keeps that smell.

NARRATOR: The castle housed Portuguese soldiers, missionaries, and merchants, but all were overseen by a governor, who regularly picked female slaves from the courtyard to bring to his room.

- The governor stands here, and he chooses the one he likes. So the woman would climb this to the governor's palace.

NARRATOR: For those female slaves who rebelled against the governor, punishment came in the form of public humiliation.

- Was there ever a revolt from the slaves that were here?

- By all means. So that is why we have a cannon ball there. They use that ball to punish the female slaves. It would be chained to your leg, to serve as a deterrent to the rest of the female slaves.

NARRATOR: For the men, the punishment was permanent.

- This is a dead cell for the male slaves. Those who were rebellious, those who tried to escape fighting the masters, they were also brought here. No food, no water until you die.

MAN: That's why they have that school up there.

GUIDE: That's why we have a crossbone and a skull.

NARRATOR: Men and women were kept separate throughout their stay. Husbands didn't see their wives, mothers couldn't see their sons.

- Slave exit to waiting boats.

NARRATOR: But they were reunited very briefly at the door of no return.

- This is the door of no return. Millions of souls passed through here, on their way to, I guess, the Caribbean, Europe, America.

NARRATOR: This seaside castle was used for captivity for more than 300 years, holding 1,000 slaves at a time, and then shipping them out every three months. It's just one of nearly 40 castles along the Ghanaian coast, which makes it impossible to count the number of lives lived in chains.