Preserved Clues (Alliance)
Preserved Clues is an Alliance-only quest for level 50 in Nazjatar. It rewards 1 reputation reward, 850 experience and money.
Description
We have found similar chests, as you describe. We believe they were left behind by one that came before the naga.
Some are even locked by odd arcane runes, the naga seem most interested in those.
I know little about them, save that we find them most often in the city ruins.
If you seek to decipher their history, I would begin there.