On the 2nd Hall level, where you play as Frodo and Gimli accompanies you, let Gimli hack the orcs at the beginning. When he's done slashing them, run across the floor and turn to your left. You will see a gap between two strips of floor. Jump
across it, and then jump across the other gap just ahead of the first one. A fallen piece of stone provides a huge ladder leading up to a ledge that an orc-archer is shooting from. Kill the orc, then head over to the blue piece of boulder. If you need to change your perspective, go ahead, but you need to push the boulder off the ledge. Another little cutscene will show the boulder come crashing down onto a narrow strip of floor that looks different from the other designs. Come back
down to where Gimli is, head over to the boulder, and push it onto a weird-looking square in the middle of the weird-looking strip. Another cutscene will show a door opening somewhere, and after this, you head across the bridges and pieces of floor until the door is reached. ( P.S. - Let Gimli cut up orcs all the way.)