Setup: Create 3 separate staging area, each with its own quest deck and encounter deck. Divide the players into 3 teams, one for each staging area. One team puts Dol Guldur into play in their staging area, attaches a threat dial to it, and sets its value to 5. Then, increase its value by 5 for each player at each stage. For the rest of the game, that threat dial is the siege tracker and it displays the city strength of Dol Guldur. Each other team removes their copy of Dol Guldur. Each other team removes their copy of Dol Guldur from the game. Flip this card over.

...there was long battle under the trees and great ruin of fire...
–The Return of the King

While Dol Guldur's city strength is 0, each Lieutenant enemy loses indestructible.

While the players are at stage 3, this card gains:"Forced: After resolving the Forced effect on Dol Guldur, the team with Dol Guldur in their staging area resolves the forced effect on the stage 3 that was not in play at any stage this round. Then, each team discards all progress from their stage 3 and advances to a new stage 3 of their choice. Each team must choose a different stage."

Response: At the end of the round, a player who controls Host of Lórien or Power of Lórien may give control of that card to another player at any stage.

If the last player at a stage is eliminated, the siege falls and the entire group loses the game. At the end of the round, if Dol Guldur's city strength is 0 and there are no Lieutenant enemies in play at each stage, Dol Guldur is captured and the players win the game.

They took Dol Guldur, and Galadriel threw down its walls and laid bare its pits, and the forest was cleared.
–The Return of the King