Saruman's servants have constructed a massive set of fell devices beneath Isengard. These engines are maintained by bands of goblin-engineers. Without their constant tinkering the whole array is likely to fall into disrepair.
'Do you feel that vibration in the ground, ${PLAYER}? Saruman has constructed...something down there. You can see some of the workings in the great rift in the western ward. I could not even begin to tell you what it is all for.
'He has goblins working on the engine night and day, though, so you can be certain it is important to his plans.
'If you can find a way down there and keep those goblins from finishing this great device of his, it will hopefully prevent any terrible surprises when it comes time to confront Saruman and his armies.'
You may be able to get down to the device array through the network of strange pipes that seem to run through the area.
Dagoras asked you to defeat the goblin-engineers working on Saruman's great device down in the rift beneath the western ward of Isengard.
Dagoras is hiding within the Ring of Isengard.
You should return to Dagoras with news of your success.