Rampart of Skulls is an outside area of the Icecrown Citadel discovered right after the Oratory of the Damned. It can be accessed through the nearby elevator or newly available Scourge Transporter. After the first group of mobs are dealt with you discover the other faction's gunship has already taken off heading towards the top. Your group must quickly fight your way to your gunship and set off to beat them to the top. Alliance players go left, Horde players go right. This is where the Gunship Battle takes place.