The world we human beings can see is only a space in the universe, called the first dimensional space, and there are a total of four spaces in this universe. The second dimension space is the demon world, and the third dimension is called the underworld, which is what we human beings call the grave. After the death of the general world and the demon world, the soul is extradited by the underworld, which is what we usually call death brought to the netherworld, and the last fourth dimensional space, is heaven, is to maintain the balance of the four worlds and the protoss living place.