Hi there, Barrel’s Supremacy!
It’s super unfortunate that you’re having trouble locating the Cave of Io!
The cave is located underground, near a small pond in the north-west of Felodrift Northlands. You may have to climb to reach it!
We hope this helps you finish the quest.
If you need any other help, feel free to ask here, in our community discussions at our forums, here or in our Discord server, here
Thanks for playing, and thanks for supporting us!