Goku Goes to Demon Land Dragon Ball : Season 6 Episode 14

Goku goes to a village whose princess has been captured by demons and taken back to Demon Land. In order to rescue her Goku must venture through the portal of the dead and defeat Shula, the lord of Demon Land. Once he does this he will be able to remove Shula's sword from the portal's entrance, thus closing it and preventing any more demons from coming through.