Warning: This video is more than a year old. But I only saw it for the first time last week when Valve's Yasser Malaika and Leslie Reed used it in a presentation about Steam for Schools.
I don't think Kotaku has ever posted this incredible interpretative Portal dance number. What makes me grin at the work done by the Ninja of the Night cosplay troupe is the way they bring the game's mind-bending moments to life on the stage. Everyone remembers the moment when first looked at themselves through one of the game's wormhole openings. The recreation of that revelation gets a big pop from the crowd and deservedly so. Great stuff.