An Undercity place and organization where promising runaways can find a home and earn a living.

There is a thieves guild here, their headquarters burrowed into a cavern wall that has been carved into an unusual shape. - Outbreak in Undercity (RPA-ADV3) 

The Thieves Guild specifically trains in sleight of hand and other skills and proficiencies for collecting treasure, etc., led by Gonk.

Members use “Finger-speak”, a type of coded language. - Backstory Codex - Separated (RPA-BC)

A generation ago the Thieves Guild was run by a necromancer, who was removed by the Night Bird;

“You look just like the Night Bird, the one who took out the necromancer that ran the old thieves’ guild.“ - Orc Thieves Guild guard, Backstory Codex - Caretaker (RPA-BC)

Gonk

Mowla

Thinfingers

Each member of the Thieves Guild in Sabek owns a Lead Medallion bearing a sword over top a moth.

It is used to gain entry into the Thieves Guild.

Gonk, the headmaster of the Guild, tests your potential as thief material while you stop in.

Following that, you can learn new skills from the guild.

The Orc guard informs you that the orphan Thinfingers was a member of the guild, until he was killed by a bloodspear.