The Isenmouthe, or Carach Angren, was a pass located in the northwestern portion of Mordor, which guarded the southern end of Udûn.
The Isenmouthe lay between where the Ephel Dúath and the Ash Mountains mountain ranges met. There it guarded a narrow passage. The pass was heavily guarded with Fortresses and watchtowers overlooking it. There was also a wall of earth built across the passage, and a large ditch dug across the entrance spanned only by a single bridge.