There were 2-3 Lugian Citadels in Dereth, and the most popular one was SE of Qalabar, where many players fought Oberoth Lugians to Gigas Lugians for easy XP. Also, these Lugians spawned more quickly than usual making these dungeons ideal XP farms.
At the end of the Lugian Citadel was a treasure chest that needed a key or a lockpick to open.