#AtoZchallenge —G is for —The Last Greenseer

From the Shadow Lands beyond Asshai to the Shores of Dragonstone and the frozen lands beyond the Wall comes the 10th anniversary of the AtoZ challenge... 

Warning: There may be spoilers

 Godswood

I don't know why the first men believed in the same gods of the children of the forest but they and their trees are kind of creepy. They carved faces of men into their weirwood trees and made a pact with the first men to never cut them down. 

Still, in the North, the descendants of the First Men worship the old gods to this day, and the sacred faces of the weirwood trees keep close watch over the faithful. Beyond the Wall, the old Gods are the only gods. So long as the trees remain in the land, the Gods have power.

The three-eyed raven hides in the roots of a weirwood, north of the wall near the haunted forest. He's creepy AF too. He is the last Greenseer with the magical ability to see into the past, present and future. 

Most of him has gone into the tree ... He has lived beyond his mortal span, and yet he lingers. For us, for you, for the realms of men. Only a little strength remains in his flesh. He has a thousand eyes and one, but there is much to watch. One day you will know.—Leaf, to Bran Stark

The Last Greenseer aka The Three-eyed Raven aka creepy old man that sees you when you're sleeping

The more I learn the more I think the three-eyed crow and the children of the forest are bad. I don't know how the Night King will be defeated only George R. Martin can solve that, but mysteries and secrets in Game of Thrones are as numerous as the gods.

Can you guess who the letter is?

He is the only living son of Balon Greyjoy and heir to the Iron Islands. When he was in Ramsay's captivity, he was called Reek.