A walk around one street
One street and a couple of side roads are enough for a short walk. Look at old shop signs, peek into a courtyard, and find a bench in the shade.
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Start near a bus stop and finish close to it. That makes it easy to head home if it rains. An hour is plenty for a first visit, with no long list of places to see.
Try the other side of the street on the way back. A different angle often reveals details you walked past earlier.