The entrance to the Underground Pass is a cave in the west part of West Ardougne. If you have started the Regicide quest you can also access it from Tirannwn, the elf land. The main purpose of this area is for the Underground Pass and Regicide quests. Throughout this pass you will encounter many tough monsters and obstacles each with their own separate requirements. The pass is also used to get a new Iban staff if you lose yours. For more information on this, look at the Underground Pass and Regicide quest guides.