From PathfinderWiki
Nation Darklands
Region Nar-Voth
Size Large town
Population 3,855
Demographics 70% duergar, 10% mongrelmen slaves, 8% svirfneblin slaves, 6% troglodyte slaves, 4% grimlock slaves, 2% other slaves
Government Conventional (military)
Alignment Lawful evil
Ruler War-Marshal Brithuan

Source: Into the Darklands, pg(s). 26–27

Fellstrok is a duergar stronghold connected via tunnels to the orc capital of Urgir in the Hold of Belkzen. Fellstrok is one of the larger duergar settlements even though it is only a fraction of the size of Hagegraf. It was only recently retaken by the gray dwarves, who continue to fight with the neighboring bands of grimlocks, mongrelmen, and other more dangerous denizens of the Darklands. Originally built by the dwarves, it was presumably abandoned during that race's Quest for Sky. As well as native threats from Nar-Voth the duergar also have to worry about a possible incursion from the surface either by slaughter-hungry orcs or their vengeful dwavern kindred.[1]

It is linked to the duergar capital of Hagegraf by the tunnel system known as the Long Walk.[2]