Citadel of Madness is a mod for The Elder Scrolls 4: Oblivion that is over a decade old. (It was first uploaded on TESAll (Released in 2013, and significantly updated in 2022 with a 2.0 release, it adds a new landmass on the Shivering Isles, a floating archipelago home to hundreds of new NPCs and where you'll find a new questline that the mod's description calls “comparable in length to any guild in Cyrodiil.”
Citadel of Madness was created by modder Lariatius and translated into English by Vorians, who has adapted a ton of Other Russian Mods It also contains 38 quests, 15 of which are side quests, and promises over 25 hours of gameplay. There are over 3000 lines of dialogue (no English dubbing, though), and a variety of new alchemical ingredients and concoctions, new dungeons, and new enemies, including bosses.
Given the connection to the Shivering Isles, you can expect Citadel of Madness to be quirky, to say the least—several of the new NPCs look like they came straight out of the Monster Factory. You must be at least level 18 to play the Citadel of Madness questline, which begins by traveling to a watchtower you’ll find north of New Sheoth on the Isles.
To install this mod, you will need to download the files from Nexus ModsThey add up to almost 900MB, which is less than some Skyrim mods, but definitely a bit on the heavy side for Oblivion. You'll also need to own the Shivering Isles expansion, but you probably already have that since it comes included with all digital versions of the game these days due to How amazing it is.
