The title, "Biblionaut," is a coined word that suggests a book-voyager, much like an astronaut or an aeronaut. That idea drives the whole short poem. The speaker has finished dinner and settled into a book, and reading becomes a journey: "in which I go far."
The second stanza shifts to night. The speaker is lying awake, and the "night road" runs alongside the path the book is taking them on. Judging by the imagery, the road might be a real one outside, or it might just be a picture of the dark hours. Either way, two journeys happen side by side: the quiet, sleepless one in bed and the imagined one inside the story.
The mood is calm, solitary, and a little dreamy. There is no panic about being awake. Instead, the speaker seems at ease, even content, with the way a book can carry you somewhere while your body stays put.