Although we've dealt a major blow to the Cultists, I'm afraid cleansing the skull was only the first step in our quest.
The Cultists seek to bring back into the world an evil that has long been eradicated. His name is Draegan. Not much is known about him. He was banished from this world thousands of years ago for unknown reasons but today the Cultist seek to bring him back. I believe that should he return, our world will never be the same.
I tried stopping the Cultists myself but one day in a battle with a Cultist Elder, I was wounded and am regrettably no use any longer. Luckily, in my encounter I escaped with something more than just my life. I stole from them a small box that I believe is of great value.
Unfortunately it is locked and I do not have a key. However, I know someone that might. He is a fisherman and he resides on jungle islands these days. You can usually find him hanging around on the shore. Tell him I sent you and that you need the key. He may ask you to do something for him first. Do it, and get the key.
Once you've got the key, open the box and hopefully you'll be able to figure out what to do next.
Lenvell will give you the Strange Box he stole from the cultists. Then you need to head to a Jungle Island with a Fisherman on it. Talk to him to start the next quest.