Go to Tarantula pond and search for an NPC called Evelyn (spawns near the pond at random locations).

She only speaks at night time. Say Willowisp Ring to her and she will ask for a pouch of willowbark from the Save the little tree quest and a Iron ring.

You can find an iron ring in Arakas chests. Once you have them return to her and say again Willowisp Ring then Yes and she will give you the Willowisp Ring.

Gain :

• Willowisp Ring