Several violet and pink shrimp swim past you as you enter the chamber. The side passages dissolve into complete blackness, as the light-emitting plants seem to line the main passage only.
The hallway ends in a large chamber, where you can see a large pedestal of black (volcanic?) stone, upon which lies a shattered glass box, the approximate dimensions of what you saw earlier.
Without yet stepping further into the chamber, you can see that inside the box is the decaying corpse of a humanoid female, dressed in fine white cloth with bracers, breastplate, and belt of green scale mail and something resembling a royal tiara upon her head.
Someone's obviously been here already.