Getting thereFrom the Shipwreck Rock Waypoint — , head northwest until the shipwreck is on your left.
Walk carefully up one of the masts leaning against the wreck, and jump down onto the deck. In the center of the deck is an open hatch - head due northwest until you reach the far end of the ship, at which point another set of stairs leads down into the hold. The achievement should appear when you stand roughly in the middle of the hold area, likely among an assortment of risen pirates.
Additionally, it can also be obtained by walking against the outside rock wall below ship directly south west of the point of interest.