Lake of Fire
The Lake of Fire is the name of an area in FoW.
Khobay the Betrayer
This quest, often shortened to "Khobay", is given by The Eternal Forgemaster after Defend the Temple of War is completed, and takes place in the Lake of Fire. Shadow Mesmer, together with his Traitorous Temple Guards, spawns in the south-east of the lake area. The goal of the quest is to kill Khobay - the guards do not need to die.
West of the lake is a bridge leading towards Tower of Strength and Forge. The enemies in the lake are mostly Obsidian Furnace Drakess and Smoke Walkers, but there are also several Infernal Wurm popups around the area. None of these foes are hostile to each other or the Khobay quest spawns, but they will fight the Shadows from ToS.