I remember as a school child being told a story (repeated by different teachers year-to-year) of an individual who crossed the Sanbatyon over Shabbos (since that is the only day it doesn’t shoot rocks up) due to some pikuach nefesh situation that allowed chillul Shabbos.
I was told this about the author of Akdamus — and that he was not allowed to re-cross, since there was no longer a pickuach-nefesh issue, effectively stranding him on the other side for life.
Of course, we know who penned Akdamus, so that’s not true.
For what it’s worth, it’s obviously either (a) allegorical or (b) historically true, but not so today (for whatever reason).
There is no river in the inhabited world that exhibits this behavior. Furthermore, it is highly unlikely that such a river exists that is (a) undiscovered and (b) large enough to create an impediment against going around.
The Wolf