This dwarf surface city is connected to the other dwarven cities through a network of tunnels carved throughout the Beor Mountains and houses the biggest river port city in the dwarves' realm, dwarves trading not just with other clans but also with various other creatures along the Âz Ragni, Ragni Darmn and connecting rivers until the Âz Ragni winds into the elves forest of Du Weldenvarden as the largest dwarven shipping port. Tarnag has been the historical home of the clans, Dûrgrimst Ragni Hefthyn and Dûrgrimst Quan, as well as dwarven from the clans, Dûrgrimst Az Sweldn rak Anhûin and Dûrgrimst Vrenshrrgn. Despite its thick ramparts, Tarnag fell to Galbatorix and the Forsworn's attacks often his war with the Riders, which led the dwarves to abandon this and the other surface cities. After Morzan's death, the dwarves returned to their fabled cities.
Dwarven engineering built Tarnag by cutting away terraces of stone upon the mountains on the north-eastern side of Kóstha-mérna constructing tier upon tier of multicoloured stones and interlocking buildings, forming a pyramidal shape topped by a gigantic dome glistening like polished moonstone—Celbedeil, greatest temple of the dwarven nation and home of the Quan clan, whose members serve as messengers to the gods. The buildings themselves are elegantly designed, often decorated with carvings of animals and other figures. At night, the city is illuminated by the multicoloured lights of the famous flameless lanterns. Eragon visited this city on his way to Ellesméra after the Battle of Farthen Dûr.