Now we must be 20 or 30 meters down? almost 20. so they have tunnels three times as deep as this. three times. reporter: what s clear here, the money, planning and preparation invested for a long siege. we re 20 meters under ground here. 20 meters, and there is a fully flush toilet. and it s even painted, has place for a light bulb and light switches. tile. the labyrinth keeps going. okay. now it s so low, we re getting done on our knees to get through. he pauses, lays out his path to victory. underground with hamas. and we have to reach this hamas core to finish them off. reporter: but those palestinian people above ground are also dying still. ....