Alix
W:O:A Metalmaster
Well, this site says it's at Hamburg Airport, but it doesn't say exactly where it is. Never been to the airport there, but I assume it's big. Hoping I won't have a hard time finding the buses.
http://anreise.wacken.com/mp5/custom?page=Shuttle&starttab=hamburg&layoutTheme=mp5_wacken&lang=en
Both times I've taken the train from Hamburg HBF, changed at Elmshorn, then either by bus or taxi from Itzehoe. If you're still keen on taking the bus from the airport and you can't find it, just ask someone at the airport information desk. They're pretty well versed about WOA.
On another note, for Summer Breeze last year, I booked the bus from Nürnberg airport directly to the festival site. I had no idea where this bus was, but I walked around in circles and found a metal looking fellow who had a clipboard with my name on it. Perhaps they have a similar set-up at Hamburg airport too...I guess just make sure you allow yourself plenty of time