The lair of the beholder, Zonthosh, is located deep below the Castle Ward of Brightridge, and accessed via the Zonthosh sewer network. According to
Thorfin Dualbeard, it was built many years ago by past
Goldstaffs of Brightridge, approximately 300 years ago.
Areas inside the lair.
Z1
Teleportation Circle
Z2
Hallway (has a Scrying Sensor monitored from Z14), hidden door leading to Z12
Z3
Zombie Beholder stands guard and will attack anyone without a Zonthosh symbol
Z4
Tunnel to the sewer network
Z5
Animate Armor guards the arena
Z6
The "Pit of Fortune and Blood" Arena, with stairs leading to the bleachers and a tunnel running underneath to Z7 (has a Scrying Sensor monitored from Z14)
Z7
Cells, usually stocked with enemies or gladiators
Z8
Recreation Hall, where guests retire after watching fights and staff eat when not working (has a Scrying Sensor monitored from Z14)
Z9
Audience Chamber, used for giving speeches and meetings
Z10
Zonthosh's Inner Sanctum, where he keeps his pet (Quilliam the hedgehog) and other valuables. Connected by a secret passage to Z12.
Z11
Zonthosh's bedroom, equipped with a Dream Nullifier, which stops Zonthosh's dreams from becoming reality
Z12
Hall of Statues, filled with petrified statues of Zonthosh's enemies, and four dead Beholders in embalming fluid hanging from the ceiling. Connected by a secret passage to Z10.
Z13
Guild Barracks, with a few old and sometimes moldy beds
Z14
Panopticus, with 4 Apprentice Wizards who watch using scrying sensors and monitor rooms Z2, Z6, Z8 and Z20. The wizards have been surgically altered by Qisdinaru so they only "sleep with half their brain"
Z15
Rest area, with nicer beds where higher-ranking members of the guild sleep, and serves as a "home away from home" or a room in a nice inn
Z16
Otto's Collection, where Otto keeps all of his valuables
Z17
Otto's Quarters, which have never been entered by the Thorfin
Z18
Thorvin Dualbeard's Workshop, with a statue pulverizer that turns statues to dust, then into plaster
Z19
Kitchen, where decadent meals are prepared for Zonthosh and common food is provided for the rest of the staff
Z20
Qisdinaru's Area, which the Thorfin does not enter (has a Scrying Sensor monitored from Z14)
Z21
Qisdinaru's prison, most likely, but it's not confirmed
Z22
Additional area of Qisdinaru's, but not much information is provided
Z23
An area sectioned off from Z20 with a portcullis, containing mortuary tables where Qisdinaru seems to work on his victims.
Z24
Qisdinaru's lab