It's not really that hard to find. The first time you're in the "device" chamber, on your way through a large archway, there are stone cylinders on either side of the exit. The right one has a handhold that's tricky to grab unless you get a running start. Once there, proceed right and follow the only path before you. The relic lies on a stone platform, and after you pick it up, you can easily return to the archway and continue the chapter.