The doors that guarded the entrance to Nargothrond, raised by its builder Finrod Felagund. They were set in the face of a cliff above the river Narog, and approached only by a narrow pathway across the cliff, making Nargothrond secure from enemy attack.
After Felagund's death, Túrin came to dwell in Nargothrond, and he persuaded King Orodreth to change this secretive policy, and to build a great bridge before the Doors of Felagund, so that his armies could more easily pass across the Narog. This was a dire error, because it gave Morgoth's forces a means to approach the Doors. After the Battle of Tumhalad, Glaurung the Dragon came against the Doors of Felagund and destroyed them, allowing the Orcs to sack the once-mighty citadel.