The Brother Tunnels, or Kronul Umthos in Dwarven, are caverns and tunnels stretching across the northern Underdark sectors Khelan and into Xalyth. They were extended in the First Kizan War. After fifteen years of work, a communication link was established between Rumaktharga and Dabul-Gind. These tunnels are said to be the only reason the dwarves beat the elves in the First Kizan War.
Kronul Umthos is a very large, extending roughly 160 miles east to west. It is a dangerous area, patrolled only near settlements and along the Kizan Line. The area's most dangerous foes are Nemestyxe's death giants.