Fetching a Fungus is a Side Quest in Sword Coast Legends. You can start this quest by speaking to Aleema Meddlebrook in The High Road.
- Search for Deathcap mushrooms.
- Bring the mushrooms to the herbalist.
Bone-Strewn Burrow. Inside the cave is the mushrooms you need. Kill the Spiders, grab them and then head back to Aleema.