Recommendations: Fantasy with a very old, creepy, mysterious forest

Hello, so as the title suggests, I would like some recommendations with an OLD, creepy forest.
So I've read The Kingkiller Chronicle and I really loved the idea of the Eld. Untouched forest with trees older than empires where the population isn't even sure what the goes on in there.
I believe there is also a similarly old forest in the Blood Song books by Anthony Ryan.
So are there other adult fantasy books where a mysterious, scary forest plays a big part in the story?
Thank you kindly in advance