In the Congo area, over a thousand years ago, the ultimate horror castle was made. The architect was a genocidal warlock king who worshipped Okubi, his culture's equivalent to the Greek God Phobos, the god of fear, and Hades, the god of the underworld and death. He was everything you think of when you hear 'evil' and 'demonic'. He was a cannibal and vampire who is responsible for the deaths of countless Africans, he made Amin look civilized. He was the king of a tribal empire of witches and warlocks who worshipped him and believed him to be the son of Okubi.
He wanted to build the ultimate palace for his otherworldly father, Okubi, and he did. He promised to grant eternal life to all his worshippers if they obeyed his every command in building this. He sent out his warriors to kill and capture all neighboring tribes and transport them to one place, dead or alive. This one place happened to be a sacred burial ground for a different tribe.
He created a simple system for dealing with the corpses of his victims: the meat was to be eaten, the blood would be used as paint, the organs would be used in rituals, the bones would be ground up into dust, then used to make strong ceramic-like bricks, and the skin would be turned into human leather.
To make matters more sickening, the same system was used for animal victims.
He built a giant castle out of bone bricks, then painted the white walls with blood, turning them red, then black.
The place was literally made of death.
He designed the place to also shelter and welcome all the typical animals of horror: snakes, bats, spiders, etc.
Thirteen years later, after it was finished being built, he used the rest of his victims as sacrifices and used the castle to perform countless demonic rituals until his death.
When he died, he was mummified and placed permanently on his throne of bones to watch over the place. The rest of his followers would be mummified and placed on the walls as permanent sentries.
The last structure in the palace built was a giant statue of the god Okubi himself, which too was made of bone dust. The statue of the god was clothed in human leather, and his giant teeth were elephant tusks.
His so called father, Okubi, never arrived to claim the palace.
The palace ever since, has been untouched by man.
Even the bravest soldiers in the continent won't go near it, for fear of everything.
The place is packed tightly with the ghosts of the victims, creatures of the night, the demons summoned in the rituals, diseases, odors, everything.