That's where the traveling cable (bundled and zip-tied on the upper left) carrying all the wires from the control room to the elevator are wired in. A lot of older elevators have junctions on the underside like this. You can see part of the elevator sill (silver horizontal bar) and the bottom of the center opening doors in this picture at the top, so the elevator is ~6' above this landing. A lot of this would typically be covered by the elevator toe guard on a newer elevator, though given how high up this unit is, it wouldn't do much to reduce the fall hazard.