Answer: a.a thought-provoking walk at night.
In this excerpt, the author describes a thought-provoking walk at night. We know that the setting is at night, because he tells us that it is "twelve o'clock" and that he can see the moon ("lunar synthesis"/"lunar incantations"). We also know that he is walking outside because he states that he is passing street lamps. Finally, we know that the walk is thought-provoking because he explains that the walk "shakes the memory."
