From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Yama Castle (閻魔 大王 の 館, Enma Daiō no Yakata; FUNimation "King Yemma's Palace"; Literally meaning "Great King Yama's Mansion") is the home of Great King Yama.
Yama Castle first appeared during the Saiyan Saga when Son Goku died and appeared in the Next World after his battle against his older brother, Raditz. From here, Goku was able to travel the Serpentine Road to North Kaio's World in order to be trained by North Kaio in preparation for the upcoming Saiyan attack on Planet Earth.
Yama Castle was covered in a thick piece of blob in Dragon Ball Z: Fusion Reborn. The thick piece of blob could only be broken when yelled at and given hurtful insults. The film also depicted the purification device that cleansed the spirits sent to Hell of excess evil energy. It was an overflow of this energy that exploded on a young Ogre that caused the creation of the monster Janemba.
It is named King Yemma's Castle in Dragon Ball Z: Buu's Fury.
- Roads to the other three Kaio’s planets exist near Yama Castle, but nothing is known about them.
- The origination of the road that the spirits use to get to Yama Castle is never shown.