I will not claim that I have fully mapped out the subterranean river that flows beneath my house; I only know that it flows northward since Bubo and I ended up in New Hampshire near Meriden. If we traveled against the current, then, would we end up in Central America?
Or, perhaps, Alabama?
Or, maybe, New Jersey.
But back to my point; there are underground rivers everywhere! Even in London. Get on your waders!