Panopticon

Panopticon, the Darksteel Citadel, is a fortress inside of the hollow plane of Mirrodin.

Description
Made from an indestructible metal called darksteel, from here the mad golem Memnarch controlled his artifact minions and watched over his world through the eyes of his creations, the myr. In his device, the Darksteel Eye, the world is viewable from the perspective of these artifact creatures.

Memnarch also had his Ascension Web built here by Slobad while he hibernated in anticipation of Glissa Sunseeker's return to the core of Mirrodin.

After Karn was infected by the glistening oil inside him, he retreated to Mirrodin's Core, from whenceforth the contagion spread to form New Phyrexia. During his time as Father of Machines, the Panopticon was converted into his throne, protected by Elesh Norn's priests, instructing him to be Phyrexia's head and keeping him in line. However, Jin-Gitaxias' servants high-jacked it to control the flow of information. With Karn's release from the phyrexian contagion, the fate of the Panopticon is unknown.

Trivia
In the real world the Panopticon is a special prison design where the jailers can see all prisoners at all times from a tower in the center. Because the prisoners cannot see the guards in the tower, they must assume they are being watched at all times even if the tower is actually empty. The idea of the Panopticon is often used as a thought experiment to explore the potential of ubiquitous mass surveillance.