For bonus mini-campaigns, maybe just some sort of thing where you can venture into a dungeon that randomizes every time.
I know a Wizard in Waterdeep who has a dungeon just like what you described, it's a dungeon called the Undermountain, all 23 levels of randomized madness, it's located under a Tavern called the Yawning Portal and it connects all the way to the Underdark, plus Deekin the Kobold can also show up as a helpful guide seeing as he completed the dungeon before...
