Under a nondescript bench seat, beside an unremarkable inner city road, grows an unassuming patch of moss. Within the miniature rolling hills of that moss, however, lives an entire world that mankind will never know, blazing along at speeds that make mayflies look like ponderous mountains. A conglomerate of civilisations figuratively dancing on the head of a pin. As abruptly as their caves and huts became cities and highways too small for human eyes to see, their world is dying. The moss patch is shrinking and the air is growing stale. Micronations rise and fall in the blink of an eye, and entire wars are fought over precious real estate in what looks like a tiny puff of smoke, or a fungus spore release.
But before their unknown universe collapses, the nano-inhabitants manage to band together and hold on to peace long enough to begin digging down into the earth. Tiny machines manned by tinier people drill deep into the bedrock and hollow out a space for themselves. There they remake their world in miniscule artificial caverns lined with the mosses of their topside lands. They are easily self-sufficient, and their technology would be the envy of any human scientist, if such scientists had any chance of discovering them. But the little world digs deeper and makes a new and better home for itself, unaware of the bigger world in which it lives, never to be seen by human eyes until the end of time.
Mokalus of Borg
PS - Not far from my office, there is a patch of moss like this.
PPS - I can neither prove nor disprove that it has microscopic civilisations living in it.