Found cedar tannin tainted rocks on the shore, followed it into the forest and found a large flat area, stepped on it, it was almost 2 meters in diameter, I kicked off the moss a bit, it looked like a large disc of brown marble.

I realized later that I was standing on a tree trunk that must have been 500-600 years old. There was no damage around it, I think this giant must have been fell more than a hundred years ago, the forest regrew around it.