Here's someone playing a Super Mario Bros "speedrun" (running through the entire game as quickly as possible), but the video of the speedrun has been composited onto the wall of a real-world building, complete with graffiti. It's hard to describe, but the effect is mesmerizing. You can see the entire SMB level on the building, with tiny Mario making his way through it. How did they do that??*
Note: to see it in HD, go directly to Vimeo.
* = Okay, it's not a mystery: they used an NES emulator, some fancy compositing software, and a lot of free time. But still. Dude.