If, on a rainy, stormy day, you take a funny little tram/train right out to the end of the very long jetty at Busselton, Western Australia,
you can walk down a spiral staircase to the bottom of the sea, and through windows, look into an aquarium - except the sea creatures are all wild, in their natural habitat.
The water is not very deep - eight or ten meters - so the power of the waves can be seen much of the way down, in the rhythmic rise and fall of a group of large fish, for example, or the waving fronds of feeding corals and sponges.
And it's lovely looking at the ocean's surface from beneath, that silvery, shifting, illusory film.
This was fascinating in itself, and very beautiful, but what stirred something deep within me was being at the same level as the surface, being able to see both above and below at the same time.
The Celts used to believe (some may still, and who's to say they're wrong?) that the boundary between land and water, be it the ocean or a river or a lake, is a "thin" place, where there is a less firm frontier between the world of spirits and the daily world we live in.
Spirits and people can move more easily between worlds, at the water's edge. This may be true symbolically and mythically, even if you can't accept it in any literal sense.
This wasn't a beach or a river bank, it was the thin place between air and open ocean. Very wonderful; very strange.