Orodruin, also known as Mount Doom, is a volcano which dominates Gorgoroth, and separates Dor Amarth in the north from Talath Úrui in the south. The northern face can be accessed from Dor Amarth. In the south, the mountain's face has blown open, creating the [[Ghâshghurm].
Landmarks
Sammath Naur
The Sammath Naur ("Chambers of Fire"), located high up Orodruin's cone, was a tunnel made by the Dark Lord Sauron in the Second Age. From the entrance to these chambers, on the eastern side of the volcano, Sauron's road led downwards and around the cone, traversing some 30 miles westward to the tower of Barad-dûr. Sammath Naur comprised a tunnel leading to an interior platform with molten lava below it, known as the Cracks of Doom.
During the Second Age, it was here where the One Ring was originally forged by Sauron, and the only place where it could be destroyed. Orodruin and the Cracks of Doom represents the endpoint of Frodo Baggins' quest to destroy the One Ring.
Amon Thaur
Amon Thaur, a hilltop temple of Sauron on the slope of Orodruin, on the Plateau of Gorgoroth, was where Sauron bound the Nazgûl to his will. Whenever the Nazgûl were defeated, they would return to this place. It is the site of the meeting of the Masters of Mordor. Iant Ruin was a bridge which once provided access to Orodruin from Barad-dûr, but it was broken in the downfall of the tower. Amon Thaur and the road from the broken Iant Ruin was guarded by Merrevail and bats under the Blood-blade, a lieutenant of Lhaereth the Stained.
Lore
The fire-mountain in the northern parts of Mordor, in which Sauron forged the One Ring during the Second Age, and into which the same Ring fell thousands of years later to bring about the Dark Lord's downfall.
When Sauron chose the land of Mordor as his dwelling-place in the Second Age, Orodruin was the reason for his choice. He used its fire in his magic and his forging, and the most famous result of his forging, and in fact the only one we know of for sure, was the One Ring, made in about the year II 1600. So powerful was the sorcery used in the making of the Ring that it could not be unmade, except by casting it back into the same fire that had forged it.
The first opportunity to destroy the Ring came in the last year of the Second Age, at the end of the War of the Last Alliance. Sauron was defeated in that War, and Isildur cut the Ring from his hand. Elrond and Círdan counselled him to destroy the Ring then (the battle had taken place at the gates of Barad-dûr, and Orodruin was therefore near at hand), but Isildur refused, and claimed the Ring for himself. So the doom of the Third Age was made.
Orodruin was far more than a natural volcano - Sauron seems to have extended his own power into it, and was able to control its fires. It seems to have lain dormant when Sauron was away from Mordor, and sprung into life when his power grew. After the Downfall of Númenor, for example, the Exiles in Middle-earth first knew that Sauron had also escaped the Downfall when they saw smoke rising from Orodruin, and an Age later at the Council of Elrond, Boromir says 'Smoke rises once more from Orodruin that we call Mount Doom'.