Dor Daedeloth was the land of Morgoth.
Dor Daedeloth, or Land of the Shadow of Dread, lay around the fortress of Angband and on both sides of the Ered Engrin. It was here that the Orcs and other creatures of Morgoth lived and bred.
The march of the Ñoldor in early First Age was halted there, when Fëanor was mortally wounded by Balrogs.
The Ñoldor then encircled the land (at least in the south), starting the Siege of Angband. It is probable that they built a number of fortresses and outposts there, but they must have been destroyed or taken over by the enemy during Dagor Bragollach.
Dor Daedeloth lay north of Ard-Galen, the great grassy plain north of Beleriand.