Dagannoth cave
From Emps-World Wiki
The Dagannoth cave is a dungeon that can be accessed by talking to the Ghost captain in the Wilderness, in level 7 just north of Edgeville. Members can also use the Lunar spellbook to teleport directly to it or to teleport a group to the cave.
The dungeon is very popular for the Dagannoths to collect Dagannoth bones.