Once those Reliquary honks got here, we panicked, and we all just started looting indiscriminately.
A lot of bad archaeology happened that day.
Luckily, Olga happened upon this small jade statue. We thought it to be a key of some sort, but can't figure out what it opens. Maybe you'll have some better luck with it.
<The statue clicks into place on the large stone slab.>
Pick up The Sentinel's Pawn before heading out. Back to the south, then down into the Tomb of the Watchers. Both The Sentinel and The Warden are just inside, standing idle. Do The Sentinel's Pawn first by taking the first right and completing The Sentinel's Game. See that quest for more information. Once done, exit the western room through its southern end, cross the central room to the east, then circle down to the southern room to find the Stone Slab.