An impressive case mod of a Nintendo Entertainment System has been making the rounds on the Interwub today. The modder managed to dissect a NES cartridge, and then put a NES into the cartridge. Does that sound confusing? Well, the pictures explain it much better. So check out the pictures.
Basically you plug in the controllers where the cartridge bit that normally plugs into the NES used to be. Then you plug your RCA cables into the back of the card. And the game cartridge gets plugged into the top of the NES mod.
Hmm... hard to describe perhaps, but very well done indeed.