Sir Arthur C Clarke wrote much of his science fiction along the same plan. A big mystery (space ship, planet, or ocean) and impact on a human scale (usually an explorer or scientist). This novel fits the bill perfectly.

Set far in the future, Earth has encountered galactic empire and retreated to nothing but a single city. The human scale mystery is a man, come of age and ready to explore (even though his fellows fear it). The grand scale is what he finds.

I believe I read the original novella (Against the Fall of Night) that this was expanded from; if I read this as a youth it didn't make much of an impact. While big in scope and message, I don't think this is one of Clarke's best works. It was a quick read, and fit the bill nicely.