Nargroth

Nargroth (Sindarin of "Fire Halls") was a watch-fortress in Mordor on the southwestern part of the Mithram Spur that

watched the gap leading into Gorgoroth as well as roads around it going to the Dark Tower and northward up the Spur.

It is not mentioned in any writings of Tolkien, but appears in a map of Mordor by him; although not the one appearing at the back any The Return of the King book by Houghton Mifflin.