15 minutes of D&D side quest brainstorming, part 1

So I need to make a side quest for two of my players in the main campaign I run. 

• The hook: 
• The goliath council member (Ira Kellouli) who is doing some legwork for them asks for a favor. Her sister, a semi-outcast swamp witch has called for aid. The witch runs a bookstore on the edge of town known for erotica and other devilish delights: her store appears to be haunted
• The journey to the bookstore: 
• Some sort of puzzle path to get there (like a riddle to find the right way)
• Also a battle with swamp creatures (come up with riddle that hints at each)
• 2 enormous tentacles (1 green, 1 yellow)
• Water does not seem deep enough for them
• 2 will-o-wisps (1 yellow, 1 white)
• If the players follow, they will lead them to a treasure of 400 gp, but also then attack them.
• Around the treasure are mossed-over bones
• The swamp witch (Evdoksia Kellouli): 
• Personality/presentation
• Flirtatious
• Constantly talking about her own novels
• Suspicious, yet excited for new customers
• Must say that Ira aka "Huggy Buggy" sent them
• Not quite all there, but just because she gets distracted by her own wares
• Physical appearance
• Goliath
• Female
• 56
• Jasper skin
• 7'5" (taller if not stooped)
• Obsidian eyes
• Long white windswept curly locks
• The bookstore: 
• Carved into a giant tree in a swamp that doesn't really make sense for the environment. 
• Lots of nooks and crannies and three levels
• Need a map so it can be a dungeon crawl
• The issue, as it appears: 
• Poltergeists (stuff gets moved, sudden falling books) seem to be plaguing the store. 
• The swamp witch fears that her devilish books have brought this upon her and perhaps she should give up her trade
• The real issue: 
• Someone has been made invisible after messing up a spell that they learned at the swamp witch's store and is desperately trying to get the swamp witch's attention for help
• The quest: 
• Undo the spell that made the person invisible
• The reward: 
• Favor of Ira Kellouli and the swamp witch
• Any book they desire
• An important contact for finding out those who seek devilish delights

(Prompt by me)

"She's Watching You" by beanpumpkin. Attribution-NonCommercial 2.0 Generic (CC BY-NC 2.0).