Ok, I've been going all over this dang castle, and every little spot that it says I can go (indicated byt the tiny "hole" in the wall on the map) is either a locked door or a rock or a big slab of concrete. I just beat the boss that gives you the lightning whip addition. Where in the sam hill am I supposed to go?

haha, just stick with it, check your map and go to gamefaqs, i just beat it w/ all monsters, all relics, all magic, all furniture & 200% yesterday.