Slayer Question

[Hollister]

I got Baby Blue Dragon's for my slayer task,
and it says I have to have a dusty key to get in,
where do I get that from?

[Cwmbran]

While you are in that cave, walk past the bridge where the chaos dwarfs are you will see some hill giants keep going into the black knights second room, then on the east side (I think) there is some jails. Kill the guard and use the key he drops on the cell with the old guy in then talk to him about exploring he will give you a dusty key.