In August in Japan, we have a special period called O-bon, when dead ancestor's spirits come back to this world. During this period, we hold many festivals or meeting in our own home town. At the end of this period, ancestor's spirits go back to another world, called Hi-gan. In case that they got lost on their way, we light many lanterns and sail them on the river for their pilots. This event is called "To-ro Nagashi."