What magical city is located above Diagon Alley?

None (Diagon Alley is a street, there is no city located above it)

Which Greek god presided over the seas and oceans? What creature was said to turn anyone who gazed upon it into stone? Which bird is famous for talking and mimicking speech? Which Olympic city introduced BMX racing as an official medal event? Which African nation has Yaoundé as the capital city?