As Antoine tells us at the beginning of Nausea, he has decided to write a diary in order to:
...let none of the nuances or small happenings escape even though they might seem to mean nothing. (1.4)
In other words, he plans on recording the details from his daily experience for their own sake, and this commitment often leads him to give us very descriptive accounts of the town he lives in—Bouville.
You can see an example of the vivid language Antoine uses to describe the shore of Bouville in a passage like this:
A puddle of light in the distance—the sea at low tide. Only a few reefs broke the clear surface. Fishing smacks lay on the sand not far from sticky blocks of stone which had been thrown pell-mell at the foot of the jetty to protect it from the waves, and through the interstices the sea rumbled. (12.140)
Remember, Antoine is going out of his way to record every single detail of what he sees and experiences. But at the same time, we quickly realize that there's more going on in his descriptions than detail for detail's sake.
In passages like the one above, we find that Antoine's descriptions of Bouville also give us a good sense of how he finds the world around him both beautiful and cold at the same time. The sea's rumble sounds poetic in his words, but its "rumble" also reminds us that the surrounding world—the "setting" of this book—is totally indifferent to human life and happiness. This tension between beauty and despair is something you can find in almost any description of setting that Antoine gives us in this book.