It's an electronic music festival played outside in the freezing cold in Montreal. Sounds like you'd just freeze yourself to misery but it's the complete opposite; it's a blast and once you are there dancing with so many others around you, you will be taking layers off. And the lineup is pretty insane for this weekend as an added bonus.
Video from weekend 1 from this year. Sorry can't embed.
http://www.youtube.com/watch?v=Wa8jyn2mGTA
Here are the main act for this weekend. Perhaps a bit too deep and heavy for some, but I love it!
http://www.youtube.com/watch?v=nTKaqhYE8IY&feature=related