The Terokkar section of the hills is generally only accessible by flight, and contains an extensive ogre-settlement that stretch to the very edge of Shattrath. It used to be abandoned, but is no longer so. It is also possible to access this area by dying, as there is a graveyard at the northern end.
NOTE: If you intend to access the areas by dying you must be in the Barrier Hills Terokkar zone not the Barrier Hills Nagrand zone. **Update: You can no longer travel from one graveyard to another when dead.**
You can get a quest - Threat from Above - from Yuula in Shattrath City to Slay any 20 Gordunni Ogres in the Barrier Hills. She is next to the Flight Master.
This is a popular farm site for gathered items such as Mana Thistle that only appear in areas that must be reached by using a flying mount.