Before you guys try this, I'm letting you know this takes a while to do. Took me about 1 hour to find and do.
First head to http://img150.imageshack.us/img150/1639/mapcn4.jpg
You want to climb to the highest point that you can in the arena in pink/red. From there, find a wallclimbing ledge (There are all over on the side of the mountain, on high points, dont reply with "AWMAGAWD I CAN'T FOINDE A LEDGE"). If you are unsure about how to get on one, or are a noob to wallclimbing, you should watch this video: in this thread.
Once you are on the ledge, you can just follow it all the way around to Orgrimars main gate.
Screenshots:
Almost there: http://img369.imageshack.us/img369/9412/onthewayce4.jpg
On the main gate, looking toward the city: http://img505.imageshack.us/img505/4950/ongatenr6.jpg
Don't be dumb like me and do this: http://img242.imageshack.us/img242/4958/dumbmovenn5.jpg