Beleriand:

The northwestern portion of Middle-Earth throughout the Ages of the Stars and the First Age of the Sun, Beleriand was made up of several regions including Hithlum, Doriath, and Nevrast. In the north of Beleriand, was Uttumno and Thangorodrim where lived Morgoth. The focus of The Silmarillion, most probably written by Bilbo Baggins, was in Beleriand, as were most of the battles and wars making up the struggle to regain the Silmarils. Beleriand was destroyed and sank beneath the waves at the end of the First Age of the Sun, during the struggle between the Valar and Morgoth. The only parts of Beleriand to survive, apart from some islands made up of mountaintops were Lindon and some parts of the Blue Mountains, the Ered Luin.