My Dear Friend,
I've been told you're on a jaunt to Toussaint. I do hope you don't overtax yourself during the Wine Festival. The effects of such exertion at your age can indeed prove most detrimental.
I've come upon some information which might be of interest to you. While browsing through a colleague's book collection, I found mention of one Professor Moreau, of Beauclair, who conducted research into witcher mutations.
The details I've come to learn are rather vague and his laboratory's location remains a mystery. Yet his journal should at least provide hints as to both. It is said he was laid to rest with it in his tomb.
I enclose a map I found in the tome I happened upon. Though less than completely legible, I trust it will prove useful nonetheless.
Should you grow tired of sampling Beauclair's ladies, wines and other exquisite delicacies, this matter might prove a fruitful diversion. Investigate at your leisure.
Your friend, Yennefer.