The phrase "sees the alley" can be substituted with multiple synonyms depending on the context of the sentence. One possible synonym is "spots the passageway," which implies that the person noticed the alley in passing. Another option is "discerns the laneway," which suggests a more deliberate act of observing the alley. Additionally, "notices the passage" and "catches sight of the lane" are two other possible synonyms that can be used interchangeably with "sees the alley." Ultimately, the choice of synonym depends on the tone and emphasis intended by the writer or speaker.