To reach the Power Pipe Ruins, travel to the Ulna Passage landmark and activate the Pressure Control Device on the west (run past the walkway to the 5th Pulse Zone and look for a red dot or just run along the walls to find it, it will not show up on the mini map). A wall will open, then climb up the wall to reach the upper level. From there head south and climb down the wall. The item will immediately appear on the map.