YOU ARE ON THE WEST SIDE OF THE FISSURE IN THE HALL OF MISTS. THERE ARE DIAMONDS HERE! A CRYSTAL BRIDGE NOW SPANS THE FISSURE.
To get the crystal bridge, you have to wave the black rod from the east or west side of the fissure. The black rod is in the debris room at the beginning of the game which can be reached from the building with the magic word "XYZZY".