In J.R.R. Tolkien’s The Lord of the Rings, the One Ring is destroyed in Mount Doom.
Mount Doom is the volcano in Mordor where Sauron forged the One Ring. Its fires are powerful enough to undo the Ring because the weapon was created there and is bound to the mountain’s volcanic heat. The mountain is therefore not merely a landmark but the only place where the Ring can be destroyed.
Frodo and Sam reach Mount Doom after crossing Mordor, guided by Gollum. Frodo claims the Ring at the Cracks of Doom, but Gollum bites off Frodo’s finger and falls into the fire while holding the Ring. Orodruin is another name for the same volcano, so it should not be treated as a separate mountain.