Write what comes to mind. If a story doesn’t come to you, start by writing a description of what you see. Who is this person? Where are they going? What are they doing? How do you imagine they walk? Talk? Do they have a speech impediment? An accent? Where are they from? Are they local? A tourist? A time traveler?
Remember: Even if all you come up with for now is a description, keep it and come back to it later. If your muse is like mine then it most likely enjoys giving you puzzle pieces that need to be fit together over time rather than the whole story all at once. You never know what will connect your pieces together, so don’t trash something just because it doesn’t seem to go anywhere right away.