Mali, in western Africa, was an impressive, expansive, and very rich empire. It had several hundred cities within it and streets made with carved stone. Mansa Musa, the emperor of Mali during the medieval period, is considered to be the richest person to ever have lived. Or at least close to it. What he did with his money was amazing. He had the Timbuktu Mosque built, which still stands. Created universities for his people, and was known for giving lots of money to poor people everywhere. Like lots of money. In the capital, they built a building called the Hall of Audience which was made with gold, wood, silver. Mostly wood, though.

Benin was fucking huge and holds the world record of the largest earthworks in the world carried out prior to the mechanical era.

The People of Yoruba also had a thing for walled cities and metal working. You can find a lot of their stuff in some musuems. I once read that Europeans were astonished that "they" could have created statues and stuff from metal.

The Zulus in southern africa were more ore less your stereotypical African kingdom (very little clothing, bows and arrows and spears, etc), but even they were pretty badass and powerful. Their King, Shaka Zulu is probably the most well know African in history.

And of course you have the Egyptians, Nubians and ethiopans. Ethiopia was actually considered the worlds 3rd most important empires for a time.

African empires were doing pretty well for a very long time, essentially.