The One Ring is destroyed in the fires of Mount Doom in The Lord of the Rings film trilogy.
Mount Doom is a volcano in Mordor, the land controlled by Sauron. The Ring was forged there by Sauron, so its destruction requires the same volcanic fires. Frodo and Sam reach the Cracks of Doom after crossing Mordor, where the Ring is finally destroyed.
The location is also called Orodruin, a name meaning “Mountain of Blazing Fire” in Tolkien’s fictional languages. Its eruption and surrounding wasteland represent the industrial and destructive power associated with Sauron’s rule.
A common confusion is Mount Mindolluin, the mountain overlooking Minas Tirith, and Mount Gundabad, a northern stronghold associated with orcs. Neither is the Ring’s destruction site. Mount Doom is specifically in Mordor.