Ok, that guy was right. At the second bonfire, there's a four legged skeleton and one with a sword on the path up. There's a pile of bones behind the sword wielding ones. Jump off the ledge right to the right of the bone pile onto a ledge (you can see the loot glowing on the platform ahead). It took me a few attempts, but I got it. Also, a bunch of bone pillars sprout up when you loot it, so be careful.
It's on a little island across a gap near the bottom of the tomb. when you see it, go up two floors and then make a running jump across the dark and hope you stick the landing. --- http://www.venganza.org/piratesarecool4.jpg