The fictional mountain where the One Ring is destroyed is Mount Doom.
Mount Doom, also called Orodruin, is a volcano in Mordor. Sauron originally used its fires to forge the One Ring, so those same fires are required to unmake it. The mountain’s connection to the Ring makes it the destination of Frodo and Sam’s central quest in The Lord of the Rings.
Mount Doom is sometimes confused with the mountain pass Caradhras, which the Fellowship attempts to cross before entering Moria. Caradhras is a natural obstacle in the Misty Mountains, while Mount Doom lies within Mordor and is tied directly to the Ring’s creation and destruction.
Frodo reaches the Cracks of Doom but ultimately claims the Ring rather than willingly dropping it. Gollum attacks him, bites off his finger, and falls into the fire while holding the Ring. Its destruction causes Sauron’s power to collapse and brings down the Dark Tower, Barad-dûr.