In 1678 John Bunyan published Pilgrim’s Progress. It describes the journey of a man named Christian from the City of Destruction to the Celestial City and was intended as an allegory of the Christian life. In 1684 he published part two, which tells how Christian’s wife, Christiana, made the same trip with her children. The second part ends with these words:
Shall it be my lot to go that way again, I may give those that desire it an account of what I here am silent about. Meanwhile I bid my reader Adieu.
Bunyan seems to be saying that he intends to write a sequel to the book. If this is true he never did so because he died four years later. But in 1843 Nathaniel Hawthorne wrote a short story called “The Celestial Railroad” which was a sequel to Bunyan’s work. It tells of a railroad that was constructed between the City of Destruction and the Celestial City so people could travel the route more easily and avoid the difficulties that Christian and his wife encountered. You can read the story here: