「Flow of fluids with widened vagina」as a place where hairy beasts dwell, sleep, stay a long time. Elements need no further explanation.
「Vast, deep and horizontal」describes an underground cave network, more often than not with internal caverns filled to the top of the rock ceiling or nearly so with 'cave fill' comprised of silt, cobbles, marl, clay and finely crushed rock, a filled orifice (田) as it were, yet how could a cavern have possibly filled to the very top of the rock ceiling? there are many such sites, more than open caves…if the fill were carried in by huge water flows and erosion, where is the water's exit path?「Same, widened vagina」(also a 'filled orifice') may have been used in addition for its shape of a「wide hole inside」the Earth's surface, or as a referent to the original birth and dwelling places of humanoids in caves and where human thoughts tend to dwell, i.e., vaginas. Contrary to past and popular assumptions, nearly all caves were likely not formed as a result of erosion from underground springs or「water flows」within rock, but instead were formed while the entire surface of the planet was covered with water and under much higher pressure than today, long prior to the appearance of any land or continents, by crushing a strata of the crust that was「all alike, the same」horizontally and not due to water/rock erosion from rushing waters such as those that carved the Grand Canyon (how did the rushing water start to rush before there was an opening in the rock? and why does that not occur anywhere within caves today? if the water were rushing so hard through the cave, why is there any cave fill remaining at all? why aren't cave walls straight and smooth with striations? cave fill does not wash into a cave from the surface. And so on):「The processes generally cited in theories of cavern formation are corrosion [erosion by abrasive action] and solution. Neither of these processes adequately explains the presence of cave fill in many caves. A new concept in cavern formation involves a possible dis-integration process due to release of former high pressure on sediments that were being elevated from depths in which they were formed. This process can account for the relationship of cavern plans to joint systems, the generally horizontal development of caves [「vast, deep and horizontal」glyph elements], and other characteristics besides accounting for the formation of cave fill in place. This avoids the problem of explaining how cave fill can be transported into caves from outside. Application of the ory of dis-integration to problems of origin of dome pits in caves is discussed, and the possibility of this explanation of the formation of caves in non-carbonate rocks is suggested.」
[ https://creationconcept.info/cavfbrd.html 2023-05-17 ]
Note the original glyph used「rock, stone」instead of「flow」to mean a hole in the stone as a CAVE, GROTTO, DEN.

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: cave; hole; zero (unambiguous spoken form when spelling out numbers)
Japanese EDRDG: den, cave, excavation
Unihan extended: cave, grotto; ravine; hole

Used within names (nanori)
とう