The Tower of Barad-dûr
The Mountain of Fire#42 (x1)
Mount Doom
Players do not raise their threat at the end of the refresh phase.

Forced: At the end of the round, each player raises his threat by 1 for each non-Fellowship character he controls.

...blacker and darker than the vast shades amid which it stood, the cruel pinnacles and iron crown of the topmost tower of Barad-dûr.
-Return of the King