Trope and Truth in The Pilgrim's Progress

In beginning his "Apology" for The Pilgrim's Progress, John Bunyan claims that he did not intend to write an allegory but "fell suddenly" into it. The implication is that the fallen human condition is itself an allegory. The Fall is a fall into an allegorical world. By writing an allegory of a spiritual pilgrimage as if it were a journey in the actual world, Bunyan suggests that the only way to escape the allegorical world (that is the actual world) is through allegory, and thus allegory itself becomes a pilgrimage.