Wall of Morannon
The Mountain of Fire#30 (x2/x1)
Location
5 (5)
Plains.  
While Wall of Morannon is the active location, each enemy and location in the staging area is immune to player card effects.

Forced: After Wall of Morannon becomes of the active location, return each enaged enemy to the staging area.

...behind the Morannon were the tunnels and deep armouries that the servants of Mordor had made for the defence of the Black Gate...
-The Return of the King