Forgotten woods

Requirements

 * Feeding Cassie quest is done
 * The Giant Plant was fought at least once, and successfully retreated
 * Fairy Grove was discovered

The trade
If you talk to the Fairy Queen about the plant, she would agree to share information... in return for some unique food she can't taste otherwise. Unlike standard gifts one requires to give her when summoning, there's no limit of how many attempts can be made.

The queen would reject most items you can offer her, not even considering them (there are special comments if you attempt to give her Golden Apple, Meat Tendril or Weird Fish). However, she would accept the Cheese, as it's indeed a new experience for her and other fairies.

The fairies would be too busy munching to pay attention to you, but when you leave the Fairy Grove, another fairy would reveal you the one and only weakness of the Giant Plant: there's a very conspicuous and very vulnerable bulb one can... rub, to make the plant leave; however, it would return eventually. It's so blatant, in fact, Lust Doll would wonder how they've missed it before.

Deep forest
The path to the north is locked by another Giant Plant, with its bulb being on the other side. Choose another path for now.

When you go to the west, you would run into a tribesman, who would run from you further to the west. To proceed further, you need to find a way around Giant Plants, avoiding or disabling them, until you reach the path to the north (blocked by another Giant Plant, but with bulb being just nearby).

This is where this quest ends for now