I'll be at this festival here in Vienna
http://www.from666hell.com/It's a bit earlier than actual Halloween, but it's said to be one of the biggest Halloween festivals in Europe.
There'll be almost everything.
Gothic/Metal/Medieval Shops, many floors with different styles of music from metal to dark wave over gothic to rock.
Many DJs, some of them being members of famous groups. (I think the singer of Finntroll will be there too)
There'll be fetish gogo dancers, DJ battles, Open Air Areas, even a Depeche Mode Special on the new album they release, a free breakfast since the doors won't close until 6AM or later.
All in all it's gonna have a lot of variety and intersting stuff.
Oh, how am I gonna dress up?
Well, I don't know.
Some black clothes, maybe a band shirt, black fingernails, and a lot of good mood