Books about a Lonely Alchemist

I’m looking for something in the medieval fantasy (or even historical fiction) genre with an isolated alchemist/astrologer/esoteric academic quietly pursuing some grand intellectual task. A little cozy, a little cold. Quiet, contemplative, slow and grounded with glimpses into the magical/mystical with Hermetic influences. Preferably close perspective on a single character with a lot of philosophical or religious musings. Anything like this out there?