The full extent of Belegaer is never made clear, but it reaches far enough to the north to be ice-covered, and far to the south.
Before the end of the Second Age, the land of Aman, home of the Valar, formed the western edge of Belegaer. Before the ruin of Beleriand at the end of the First Age, the sea was narrow and ice-filled in the north, forming the strait of Helcaraxë, the Grinding Ice. It was thus possible to cross from Aman to Middle-earth on foot, though with difficulty, as did Fingolfin and his people of the Noldor when fleeing Valinor.
At the end of the Second Age, when the seas were bent and the world was made round, Belegaer washed "new lands", and only the chosen could find the "Straight Road" to Valinor.
Belegaer has several islands and island chains: