Mirkwood / Greenwood, Dol Guldur - In the Third Age the ancient forest of Greenwood grew dark and choked with ivy and became the dreaded Mirkwood. As related in The Hobbit, it was here that Bilbo Baggins and the Dwarves encountered the giant spiders. In the southwest corner of Mirkwood stands the fortress of Dol Goldur, Sauron's hiding place and the source of the forest's blight.