Citadel of Madness is mod for The Elder Scrolls 4: Oblivion that's over a decade old. (It was first uploaded to TESAll in 2013, and significantly updated in 2022 with a 2.0 release.) It adds a new landmass above the Shivering Isles, a floating archipelago where hundreds of new NPCs live and where you'll find a new questline the mod's description calls "comparable in duration to any Cyrodiil guild."..
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More than 10 years after its creation, massive Russian Oblivion mod Citadel of Madness has been translated into English
Source: PC Gamer (opens in a new tab)