The Undercity was originally an area far beneath the palace of the City of Lordaeron, a city of the human continent and kingdom of Lordaeron. The area consisted of the dungeons and sewers of the city, as well as the ancient crypts and catacombs of Lordaeron's royalty. After Prince Arthas Menethil killed his father, King Terenas II and became ruler of the City of Lordaeron, he made it the capital of Lordaeron and made orders for the catacombs of the Undercity to be expanded. However, this work was left uncompleted as Arthas left the city for Northrend to fight against the Lich King and his army of the Scourge.
After Arthas' exodus from Lordaeron and Sylvanas Windrunner breaking free of the Lich King's control and founding the Forsaken, Sylavana (alongside her ally Varimathras) defeated the dreadlords controlling the city, brought it under her control and ordered her Forsaken to finish the expansion of the dungeons below Lordaeron. The Forsaken made the Undercity habitable and took up rule over the surrounding countryside.
The entrance to the Undercity is surrounded by the ruins of Lordaeron and those who wish to enter the city must pass through the ruins of the throne room of the palace of Lordaeron and descend down one of the three elevators, guarded by two abominations.
The city itself is a comprised of a number of roughly symmetrical quarters: The Apothecarium, The Magic Quarter, The Rogues' Quarter and The War Quarter. These quarters are arranged around a central area into which the entrance elevators of the city run; The Trade Quarter. South from the Apothecarium entrance is the entrance to the Royal Quarter and branching off of the West of the city is the Sewers. The area that runs between the quarters is known as the Canals.
The city is dark, dreary and is described as cold, smelling of corpses and having "an evil feel". The city also does not change its appearance for any festival except for Hallow's End. The canals are filled with a mysterious green slime and the deepest areas of the cities are occupied by spiders, oozes and other similar creatures.
- Despite the Undercity being the home city of the Forsaken, the crest that appears on the in-game map of the city is that of the Scourge.