Individual modes

Hell is not underground. The realms of rebirth are merely individual modes of perceiving and experiencing the one ordinary world we call reality

Due to the fluid and fleeting nature of consciousness in practice there are countless realms. The six realms are degree of suffering a category, there are in fact numerous subcategories such as crushing hells, cutting hells, hot hells, cold hells, etc. Also the divine realms have countless sub-animal words, where we find countless ways of living and form of life varying in degrees of suffering and pleasure.