Key to the lunarium facing the lake on the second floor of Byrgenwerth College.
In his final years, Master Willem was fond of the lookout, and the rocking chair that he kept there for meditation. In the end, it is said, he left his secret with the lake.
It is found near the top of the Byrgenwerth Building, on a counter.
The Lunarium Key unlocks the door to the Lunarium of Byrgenwerth. This allows access to the lookout where Master Willem is sitting on his rocking chair.
A Lunarium is a device that allows one to observe the different motions and stages of the moon. In this case, the Lunarium itself is located on the top of the building of Byrgenwerth, but allows one to also access the Lookout.