Sezzherei's Lair
From Drunkapedia
A gem that summons a portal to a dungeon that houses a Margul named Sezzherei. You can use the gem to go kill Sezzherei and obtain a quest helm with minor salvaging on it or alternatively the gem is required in order to complete the quest to get flagged for Vissidal Island.
Obtained by:
Killing Fallen Creatures in the VoD or Caul. Drop rate is nearly 100%.