Skyrim mod The Rot Below promises a '3–6 hour dungeon experience' and is fully voice-acted

Sometimes in Skyrim you wander into a hole in the ground, fight some draugr, defeat a dragon priest, collect a shout, and leave via an exit that conveniently loops you back to where you came in. Sometimes you end up in a gloaming fungal underworld and only emerge hours later barely remembering what the surface looks like. If you'd like more of the latter experience, The Rot Below is probably the mod for you.

Impressively, it's the first mod by TheCrowKnight, who says it contains "A host of terrifying new enemies," as well as "Three boss battles" and "over 350 professionally voice acted lines." Most of those voice lines presumably belong to the villainous lich Malkifer and a bard named Adabelle you'll be tasked with rescuing, though the credits also include "The Undead Blacksmith".

The Rot Below also includes new magical items, including glowy enchanted swords, and conjuration spells that let you summon new undead servants. Maybe even some of the mushroom-headed skeletons who appear in the trailer. There's new music too, so if like me you muted Skyrim's repetitive score a hundred hours ago, maybe turn the volume back up for this one.

You can download The Rot Below from Nexus Mods. Its questline will trigger after you hit level 30, and you'll need to find a journal that should spawn in the room of any court wizard to kick things off. Maybe bring a follower with you as well—this is one of the nice quest mods that doesn't demand you leave Lydia or Inigo behind before you embark on it.