Final answer:
Robert learns about what a cathedral looks like through descriptions of architectural styles and observations of light and shadow on different cathedrals, such as the Cathedral at Chartres and Durham Cathedral.
Step-by-step explanation:
By the end of the story, Robert learns what a cathedral looks like through the descriptions and experiences shared by others who visit and observe various cathedrals.
Such discussions include the architectural evolution from the Romanesque to the Gothic style, as expressed in the Cathedral at Chartres with its columnar jamb figures and High Gothic elements on the south porch.
Additionally, reflections on cathedrals like that of Notre Dame de Chartres and Durham Cathedral reveal how sunlight and shadow play upon their facades, adding to Robert's understanding of their aesthetics and design.