[Hells Forge]

Please for the love of god someone tell me what to do in chapter five. Ive killed the high priest throiskan over whatever, ive made the histachii brew. Ive put Mandel's spirit to rest, ive killed the fake nathinel, made wyvrens poison, expolored the whole area on every level and lowered the bridge on third level! There's this wierd door that has the tubes running into through the wall. Its right by the exit up to the 2nd level when you come into the third and i cant figure out what to do with it. Someone help me get to chapter six please!