The Cultists' Crypt

The Cultists' Crypt is not an official quest, but because it has similar characteristics to other small quests in the game, it will be treated in the same manner as an official but optional quest. It may take place either in Acts II or III when Geralt finds the Letter for Knight Eric and the Lionhead Spider crypt key on a dead knight in the Sewers under the Temple Quarter.

Walkthrough
In the Sewers under the Temple Quarter you will find a dead body of an Order knight. On his body there is a letter addressed to "Knight Eric", describing the location of a secret base of operations for the Lionhead Spider, and a key which will unlock the gate to the Lionhead Spider Cultists' lair.

The cultists' crypt is fairly well populated by fanatical Lionhead Spider cultists, jealously guarding their stashes of alchemical ingredients, jewelery and money. The crypt is also moderately rich in Sewant Mushrooms. There are several Aardable stone walls in the crypt that you must break through in order to assault the cultists and claim their valuables as your own, as well as two Circle of Elements: Circle of Lifeless Air and Circle of Inner Fire.