I believe it is the fountain. We made need the water to bring down the barriers.
The fountain. You entered this dungeon from the south, descending stairs. At the northern end of the stairs was a vestibule with three doors. The northern door leads to the fountain, which has a visible (but largely obscured) field surrounding it. Something is suspended in the field (and some of the characters have the distinct impression that the floating object is actually the elven woman whose screams magically echoed through the dungeon), but you cannot see the fountain clearly because a second field surrounds the entire chamber and also blocks off the western edge of the vestibule, preventing you from accessing that door. The eastern door of the vestibule was the one through which the goblins entered when they ambushed you. And you explored that path (the only one currently accessible), leading you to the store room you're in now. The inner forcefield seems to be a column of bright light covering the fountain. The outer forcefield is green and murky (more translucent than transparent), so visually making out details is difficult.
The northern door is wide open, but the forcefield surrounds the chamber.
