In The Lord of the Rings: The Fellowship of the Ring, Caradhras is the mountain pass where the Fellowship is trapped by a storm. The group attempts to cross the Redhorn Gate in the Misty Mountains.
The route becomes impassable when heavy snow and violent weather block the Fellowship. Aragorn and Boromir try to clear a path, but the party eventually turns back. Gandalf then suggests traveling through the Mines of Moria instead.
In the film, the storm is associated with Saruman’s intervention, while the wider mythology also presents Caradhras as a hostile mountain with a dangerous will. The pass itself is named after the mountain, which is also called the Redhorn.
Caradhras is not a fortress or a city. It is a peak and mountain crossing, and it should not be confused with Mount Doom, where the Ring is destroyed.