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…