Stuck at endgame

[radiant ingot]

So after killing the ||second boss|| I just cant figure out where to go. I went through that ||cave|| and picked up a few items but then I hit a ||rock wall||. Is this intended or is it that I'm missing something? ||(Also i know I'm supposed to pick up a artifact, does not help me though)|| 😦

[south cobalt]

You are missing a sort of "key" i will dm you a screenshot cuz i cant upload it here?

[south cobalt]

Add me as a friend and i will dm you right away