The Manor Key open Manor of the Immortals dungeon.
The Manor of the Immortals is a medium to high-level dungeon designed for fairly powerful (level 20 with defense maxed) characters.
The dungeon is a source of Potions of Attack, Holy Water, and the Purified Priest UT set.
Entrances to the Manor of the Immortals are commonly dropped from Kage Kamis, an uncommon enemy found in Dead Forest setpieces in the Highlands.
This dungeon must be completed to earn the ‘Tunnel Rat’ fame bonus.