Myth operates very comfortably in the realms of the impossible, and Graeco-Roman literature from Homer and Hesiod onwards had a ready-made repertoire to draw on. Within a restricted compass, may sample the impossible journeys to and from the Underworld and take a glimpse of the world above. The Underworld is an obvious starting-place for fantasy; unlike the lore of exotic lands, no distorting reports can underlie whatever fictions are placed. But such fictions soon run the risk of conforming to a more or less predictable series of situations. A number of basic motifs will underlie the katabasis, the journey down itself. Heaven or Olympus is a good deal less stereotyped than the world of the dead, perhaps because mankind has normally a good deal less business there. There are rather fewer attempts, for example, at celestial topography, though again, as early as Homer, the world of the Olympians is imagined and presented often enough.