SPOILER get your beetle and fly through the passage and pick up the bomb then drop it on that rock thats impeding your way SPOILER*I'm a bit stuck on the 4th dungeon. (Ancient Cistern)
I'm stuck near the boss key, in the room with the stone that says "A gemstone shines deep within the eye. Strike it to shut the mouth and dam the flow."
I did that, but I don't see how it helps me. I can't seem to find a way to get near enough to the big rock to blow it up either so I can get to the spinning things with vines on them.