Looking over the quest in Great Destroyer, it doesn't appear there are any boulders that you can't push out of the way. The treasure room with the boulders (I'm assuming) is the one you're referring to. There is supposed to be a block pushing puzzle in there but I'm having trouble getting that puzzle to work so I just lowered the rope on the side with the treasure right to the floor. When it is working, you would have to push the boulders to make a path for you to cross over. I hope that helps for the time being. If there is a different boulder you are refering to, something that is impassable and is blocking the path somehow, please do let me know.