From HGWiki

Lots of ant like formians including casters and the Weaponmaster who has a low DC Devastating Critical attack and the Formian Matriarch (level 22 accomplishment (see Accomplishments)), best to keep her occupied as she hits very hard, the key (not consumed) to get into her room is in a chest (unlocked) in the other room. The altar in her room gives the Ring of Passwall to level appropriate characters.
Note: To get to the Formian Matriarch you will have to transit through the Lower Mine zone as her area is not accessible directly through the first part of the map.

Contents 1 Items 2 Rest Spawn Chance 3 Creatures 4 Exits

Items

• Ring of Passwall

Rest Spawn Chance

High

Creatures

• Formian Worker
• Formian Guard
• Formian Adept
• Formian Taskmaster
• Formian Matriarch

Exits

• Giants Lair
• Lower Mine