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[BASGTA]

So uh,

Spoiler below!

I've heard it's in a barrel, and that you need to break it open, but I've broken open every barrel, the only thing I have found is some gun powder.

EDIT - Alright, I got it, but what am I suppose to do with it now?

[Thaliur]

Spoiler below!

If I understood you correctly, you should now have fashioned the string into a fuse. Somewhere in that area you should see a TNT barrel. Using this and your newly-crafted fuse, you can blow up the cave-in.

[stAtic15]

Wet it in baxtrin then put it in the gun powder, and then use it on the TNT barrel to blow up the cave-in, like Thaliur said.