To go under a river: there's a strange thing to do, a really weird idea. To cross a river, to ford it, wade it, swim it, use boat, ferry, bridge, airplane, to go upriver, to go downriver in the ceaseless renewal and beginning of current: all that makes sense. But in going under a river, something is involved which is, in the central meaning of the word, perverse. There are roads in the mind and outside it the mere elaborateness of which shows plainly that, to have got to this, a wrong turning must have been taken way back.
-- Ursula K. LeGuin