Aaron Webber, Sega's community manager, went on a three weeks vacation, and came back to find his cubicle completely remade into the Green Hill Zone from Sonic the Hedgehog. Check out the video, the attention to detail is impressive.
The best part is the rings hanging in midair, followed by the blue Robotnik/Sonic sign that spins as you whiz by at the end of the level. The clouds, trees and ramps all show a great deal of effort, too. This probably took a good portion of the workday, if not all of it.
Webber's a good sport about it, and why wouldn't he be? I want to work in Green Hill Zone, too!