Nan Dungortheb
From Tolkien Gateway
Nan Dungortheb was the dreadful valley in northern Beleriand that ran west to east between the haunted mountains of the Ered Gorgoroth and the enchanted northern marches of Doriath.
Nan Dungortheb means "Valley of Horrible West" in Sindarin (from nan = "valley", dûn = "west", and gortheb = "horrible").