A loxodrome
or rhumb line, here shown as a boxy tube. If you sail a ship from
one pole to the other while keeping a fixed angle (unequal to 0°
and to 90°) with respect to the meridians of longitude, i.e. keeping
the same bearing, you'll get to the other pole after an infinite number
of revolutions, with the distance between them decreasing closer to
the poles.
