|Location||South of Endor, north of Hither Lands, coming from Belegaer toward the Straits of the World|
The Great Gulf was created after the destruction of the Two Lamps by Melkor and in the following war, when the Valar widened the great sea Belegaer. The Gulf started at the southern end of Beleriand, and from there flowed east all the way to where later was south Gondor, where a narrow strip of land separated it from the Sea of Helcar.
After the War of Wrath at the end of the First Age, the Great Gulf drained the Sea of Helcar and effectively disappeared itself, because much of Middle-earth was drowned. Only its eastern end remained, and became known as the Bay of Belfalas.