In Japan, people think that water sometimes becomes a border to divide two different worlds. Kamo River, which runs through Kyoto City, also used to be thought as the border to separate the world for the living from that for the dead.
There was a crematory in the area called Toribeno. This area is located at the east side of Kamo River. In the medieval era, the east side of the river was not populated yet. Therefore, people might thought that going over the river meant going out from this world.
It has been said that people walk across Sanzu River to reach the other world when they die. This idea probably comes from Japanese Buddhist tradition. Anyway, even though Kamo River is not Sanzu River, locating a crematory beyond the river implies their understanding of this place as the other world.
If you walk Matsubara Street (松原通り) toward the east, you will notice many shrines and temples along this street. Go across Kamo River and stop by Rokudo-Chinno-ji temple (六道珍皇寺). This is an entry to Hades (Meikai no iriguchi, 冥界の入り口), but you do not have to be scared. (T)