A. A playable rainbow land? (Hiya, Spike.)
B. A combo with Power Conduit? ('Sup, Johnny.)
C. Or do you see an interesting peek at the interior of the plane of Mirrodin?
If you answered C, this Magic Arcana's for you.
The illustration on Mirrodin's Core shows the material and structure that makes up the mostly-hollow shell of Mirrodin. Let's take a closer look. Here's a description of the interior of Mirrodin from the Mirrodin Style Guide:
"The interior of Mirrodin is a vast, featureless expanse of silvery, dull metal. Maybe it looks hammered or dimpled slightly, or otherwise irregular somehow. The only features of the landscape are the mycosynth, the occasional artifact creature, and Panopticon. The interior is lit by the mana-core sun, which washes everything in intense, pure-white light. (The mana core appears as a giant sphere of pure white plasma suspended at the nucleus of the planar sphere. Occasionally it flares, arcing toward the interior like an enormous lightning bolt.) Illustrations of things on the interior should be visually distinct from things on the surface. Things will look washed out, overexposed, and/or mostly desaturated due to the intense blue white light emitted from the mana core."
And here is John Avon's concept illustration based on that description:
Neat, huh? And here is a close-up of Greg Staples's piece that appears on Mirrodin's Core: