Die shot: http://i.imgur.com/Unb9ng0.jpg
If you pick up a packaged CPU, you can't see this surface unless you rip the package apart. In a package, this surface is mounted face down on a tiny PCB which connects the wires to pads or pins for the socket that the CPU is inserted into, and also, a metal lid is slapped on top of the silicon chip (with thermal paste in between). Then a heatsink is slapped on top of the metal lid.
Teal rectangles on right (in between squares): L2
Orange mass on left: GPU
Blueish rectangle on bottom: DDR interface (?) Possibly L3, I forget if these actually have L3.