What four directions which are not described by 四处 are described by 八方?
四方 / 四处
现代汉语大词典

东南西北四个方向


四处 (or 四方) = north, south, east and west


八方
古汉语大词典

四方(东、南、西、北)四隅(东南、东北、西南、西北)的总称。


八方 = (north, south, east and west) + southeast,  northeast, southwest and northwest


四方 and 四处 can be used interchangeably. There is also a third one: 四面.
Another word you might want to know:

十面 = ((north, south, east and west) + southeast,  northeast, southwest and northwest) + up and down.

八处 doesn't seem to be a thing, but 八面 does exist.