Mount DoomMount Doom - The Mountain of Fire, called Orodruin in Sindarin.  It was here that the One Ring was forged and, ultimately, destroyed.  The Siege of Barad-dûr at the end of the Second Age was also began at the foot of this mountain.

 

"Now Sauron prepared war against the Eldar and the Men of Westernesse, and the fires of the Mountain were wakened again.  Wherefore seeing the smoke of Orodruin from afar, and seeing that Sauron had returned, the Númenóreans named that mountain anew Amon Amarth, which is Mount Doom." ~The Silmarillion (Of the Rings of Power and the Third Age)