This thread uses a similar trick as the [How to: Pics and Video]Get into Old Ironforge using The Chopper. and [Exploit] Hack through Walls with Motorcycle Mount threads. Also I checked for similar threads and found nothing.
I figured after years of lurking I'd actually try and post something. This is a useful way for hordes to fish in Ironforge without worrying about being ganked non stop. I did this as an Alliance since I'm way too poor to be able to afford a chopper on both my chars.
You're gonna need a chopper or a horde friend who doesn't mind sacrificing himself so you can get into old IF.
Assuming you're horde, you're going to want to just ride into Magni's room and get as close as you can to the left door. You should get auto dismounted and thrown behind the door. I would also suggest you keep your armor on in case you get any chasers.
Then just keep running down until you get to the entrance to Old IF:
This is the ledge we will be landing on to fish:
And take the path all the way down to the bottom and run to the left door:
Once you drop down you can fish without any hassle
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Anyway hope this is useful to someone.