When it comes to describing a specific location or direction, there are numerous synonyms for the phrase 'down one alley.' Depending on the context of the sentence, you can use terms like "through a narrow path," "along a solitary passageway" or "down one narrow walkway." You can also say "towards an obscure alley," "into a dimly lit alley," or "down an obscure alleyway." If a more poetic approach is desired, you could use phrases like "down a shadowy lane," "along a secret passage," or "into a hidden grotto." Ultimately, there are many different ways to express the concept of progressing down a particular path, so feel free to use the synonym that best matches your voice and tone.