Father Seren examines the symbols carefully, glides his hand along a symbol and the slab parts smoothly, revealing a chamber beyond. This one seems oriented the same as the chamber above: parallel with the earth's surface, so in theory there will be an awkward but non-lethal gravity shift to walk into the room, as there is a very short right-angle vestibule leading into the room.
The heat and humidity are almost unbearable here, and the repeated whine and whump! are painfully loud. The room is dark, lit only by three glowing plates set into the floor, bound by strips of white light on their borders. The one on the right is surrounded by a shallow moat of some clear liquid, no more than a foot across, being fed by a small trough of the stuff that pours from a pipe in the wall. The surface of that plate shimmers and gleams and writhes slightly, like something is under it.
The one on the left throws a shaft of light straight up to the ceiling over a hundred feet above, and occasionally crackles of light that resemble the symbols you've seen leap across the floor from this plate to the other two and back again.
The plate in the middle seems to be the source of the sound you've been hearing. As the whine builds, the light in its center glows, and the whump! sound is a huge discharge of energy that springs upward and then takes a sharp turn south along the ceiling and out of sight. The power in this room is enough to make everyone's hair stand on end.