For a narrow alleyway, the best urban outdoor furniture is the kind that keeps a small footprint and can move or fold away when people, deliveries, or wheelchairs need to pass. I would start with wall-mounted fold-down benches, because they give people a place to sit without permanently taking up floor space. Choose shallow benches, ideally no more than about 40–45 cm deep, with rounded edges and a simple backrest or no backrest at all so they do not make the alley feel tighter.
A folding bistro set is another practical choice. A slim table with two lightweight chairs works well for short coffee breaks or lunch seating, and the whole set can be folded and moved aside when the alley gets busy. Stackable stools are also useful because they are easy to tuck under a ledge, into a corner, or beside a doorway. If you want something more permanent, a built-in bench along one wall can work, but it should leave a clear walking path of at least 1.2–1.5 metres.
I would also consider modular planters with integrated seating. They help define the seating zone, add greenery, and keep the alley feeling tidy without blocking sightlines. Materials matter in tight urban spaces, so powder-coated aluminium, galvanised steel, weather-resistant wood, and anti-slip surfaces are smart choices. Avoid bulky picnic tables and deep benches that sit out from the wall, as they tend to catch pedestrians and make narrow alleyway seating feel cramped. A mix of a fold-down wall bench, two stackable stools, and one narrow bistro table is usually enough to make the space useful without sacrificing movement.