An alchemy laboratory, where an alchemist brought in from outside of Aeternis worked to try and uncover further secrets of the grail. While he did manage to create a potent poison and the means to neutralize it, he perished by his own hand when he mixed a little too much red salt into his experiment. The resulting explosion killed him and coated his body in a thick layer of incredibly poisonous toxin. The knights never managed to neutralize it.
This is a small room, containing chemical apparatus and various old reagents. Philip is encountered here for a second time and if he likes you, he will share more information about Aeternis and its inhabitants, as well as warn about the poison that covers the late alchemist.
The room contains one of two shield IIs, which can be removed by using aqua fortis on the growth that covers it. To get the key ring and unlock access to the attack tunnel, you need to neutralize the poison by placing the flask in the alembic by the entrance and using the decoction of moon, earth blood, and aqua fortis (found on The Tempest). Then use the flask on the body and get the key ring. It unlocks the other door in the lab.