The spherical curve taken by a ship which travels from the south pole to the north
pole of a sphere while keeping a fixed (but not right) angle with respect to the meridians. The curve
has an infinite number of loops since the separation of consecutive revolutions gets
smaller and smaller near the poles.
A series of spherical spirals are illustrated in Escher's woodcuts "Sphere Surface with Fish" (Bool et al. 1982, pp. 96 and 318) and "Sphere Spirals"
(Bool et al. 1982, p. 319; Forty 2003, Plate 67).