imagine your natural environment had no bottom to it
there was up
up came to the end of your environment and other took over from your own
the one that took over was different, you could not breath in it
it had color, sensation to your senses, was thinner and other life forms unknown to you lived in it cos you saw them on occasions
that was known about
as where the sides of your environment
the ended the same way as up did
same place
solid something which when you went upwards alongside it you came to the up place
that was known about
it was below that was unknown
it went forever down past any place someone had been to it`s end
if it ever did end