Here's what the art for Panopticon looks like, shorn of its Planechase trappings.
On Earth, a "panopticon" is a structure for a prison in which the guards stay at the center and can see into any cell at any time. On the plane of Mirrodin, it's a massive tower (occupied by Memnarch) from which the entire plane can be viewed. You might know it better as the Darksteel Citadel.
Ah, but what about those growths that are all around the tower in the Panopticon art? You can see a couple of them in the distant background of Darksteel Citadel, but there's a better view of them on Mirrodin's Core.