No spider boss showed up for me?

[Drakasun]

Hi

I did find the circle of stones, I had forgotten it was on the bridge!! So I've now finished the game I found a cave somewhere (can't remember which island) and it was just empty, it had a red vortex thing in front so I thought it must be significant but there was nothing in it and I don't remember having a conversation with any character about a giant spider. Maybe there was a glitch in this quest for me?