Tol Dagor is a dungeon whose entrance is located in Tiragarde Sound in the World of Warcraft game. The level range for the normal dungeon is 110-120. The dungeon contains 4 bosses. The end boss of Tol Dagor is Overseer Korgus.
Tol Dagor is a prison island off the east coast of Tiragarde Sound. It won't appear on the main Tiragarde Sound map but will appear on the continent. You will need to swim out to it for the first time and then get the flight point for it.
The dungeon is available on Looking for Group (LFG) at 115 for Alliance and at 120 for the Horde.