Solemnace

Solemnace is a Tomb World ruled by Trazyn the Infinite, an Overlord of the Nihilakh Dynasty. Its galleries are famous for displaying some of the greatest artifacts and technological wonders in the galaxy and have been visited by Necrons of almost every dynasty before the Great Sleep. The Tomb World is also known to contain one of the greatest document collection in the galaxy, such is his size that even rivals the Black Library of the Aeldari. The planet itself is an artificial construct, essentially a planet-sized Dyson Sphere whose outer shell consists of untold amounts of nano-machines. A series of "mirrors" exist above the planet which collect Solemnace's excess energy and redirect it back to form an artificial sun and atmosphere. Beneath the outer nano-shell are vast prismatic galleries, where Trazyn's many collections exist in suspended animation.
Solemnace is mostly dormant, with Trazyn only needing a small team to help him manage the planet. Among his team, he employs Architect-wraiths, Lychguards, and an Arch-Cryptek called Sannet who serves as Chief Cryptek and the curator of the Solemnace collection.
Trazyn has also connected the Tomb World to a hidden Sub-dimensional reality bubble via Reality-Tethers. It is only able to be entered and exited by the Overlord or his minions and contains a stronghold, named Sanctum, which holds reality-warping arenas, that are replicated from those used by the Imperium. Trazyn has placed renowned warriors there, which he has fight for his amusement, though the Overlord has promised to free whoever emerges as the ultimate victor between them all. However due to the advance technology available to the Necrons, Trazyn is able to heal the warriors of even the most lethal wounds and send them back into the fray. Even should someone actually win, though, the Overlord has no intention of keeping his promise of giving the warriors their freedom. Instead, the arena winner will have the honor of taking a place of pride within Trazyn's latest exhibit on Solemnace.