From 1d4chan

"You will never find a more wretched hive of scum and villainy. We must be cautious."

– Obi Wan Kenobi about Mos Eisley, which compared to Skavenblight is a fucking paradise of love and harmony
Skavenblight, looking like it came out from a Samurai Jack episode

Skavenblight is where the giant rats make all of the rules would be the "capital city" of the Great Underground Empire, at least if it were possible for Skaven to agree on something as important as a capital city. The best way to describe it is a giant pile of rats that explode (both the rats and the pile). It is located north of Estalia and north-west of Tilea, or where Andorra would be in the Old World. Basically imagine living in Liverpool but with a better crime rate.

Geologically, Skavenblight resides in the middle of a fetid swamp filled with dangerous wildlife, which fill the swamp with dead Skaven and skavencrap, which fertilize plants which produce black rice-like grain for the rats to eat, perpetuating a gruesome cycle of unashamed cannibalism that represents their society unnervingly well. Skavenblight proper is a ramshackle rat's nest of factories, slums, warpstone generators and narrow mines laid out in no particular order with little forward thinking as to how these structures will interact with one another. These teetering buildings of rusted metal, mud, stone, reused bricks and rotted wood are held together by the flimsiest of rope and are perhaps as big a danger as the deranged ratmen that reside in them. Old towers crumble just as quickly as new ones are erected, and new tunnel systems are carved out and collapse so frequently that it forces the Skaven to rely on scents and musk in order to find their way around. The labyrinthine layout combined with the unorthodox and unstable architecture make Skavenblight nigh impenetrable to foreign adversaries, further proof that the only enemy truly capable of dealing a decisive blow to Skaven are the Skaven themselves.

Skaven would later survive End Times by teleporting Skavenblight to another dimension. When Horned Rat became Great Horned Rat he immediately drew Skavenblight into the Warp and created more of his Daemons. Skaven had a golden age where there was Warpstone everywhere to be found, they had the direct blessing of the Great Horned Rat, and unlimited space and potential around them. They promptly did the impossible and somehow dug so deep that part of the Warp collapsed into Skavenblight which collapsed into the material realm which is now made up of eight "nearly infinite" planes made of the former Winds of Magic. Skaven now have access to all of reality at once, and can appear everywhere from beneath Sigmar's throne to beneath Khorne's throne. As can be expected the tunnels are not stable and thus only the Skaven are willing to use them usually, as even immortal and deathless Daemons can somehow vanish into the space between spaces never to be seen again when Skaven are involved.

Also at some point in AoS, they renamed Skavenblight to the sadly less interesting Blight City.

Coincidentally, the infinite inter-dimensional ramshackle maze that is Skavenblight would make for a pretty awesome setting for a Warhammer Quest game if GW were to ever recognize the potential for basically a tabletop version of Vermintide x10, infiltrating the Skaven empire to recover stolen artifacts or stop a particularly insane (even by Skaven standards) doomsday plot.

Regions and Areas of the Warhammer World
Areas of The Old World: The Empire of Man - Bretonnia - Albion - Estalia - Tilea - Kislev - Norsca - Border Princes - Worlds Edge Mountains - Karak Eight-Peaks
Areas of The New World: Naggaroth - Lustria
Areas of The Eastern Lands: Cathay - Nippon - Ogre Kingdoms - Dark Lands - Kingdoms of Ind - Khuresh - Eastern Steppes
Areas of The Southlands: Nehekhara - Araby - Badlands - Marshes of Madness
Other Areas of the world: Ulthuan - Athel Loren - Chaos Wastes - Skavenblight - Lost Isles of Elithis
Main bodies of Water: The Great Ocean - The Far Sea - The Sea of Dread - Inner Sea of Ulthuan