Why it is worth a whole day
Most of the coast's sights take an hour or two. Galle Fort absorbs a day without trying, because the pleasure of it is not a checklist but a texture: lime-washed walls, columned verandas, louvred teak shutters, all of it the same architectural family as the villa you left that morning. The Dutch line runs straight down the coast and through both buildings, which makes the fort a strange kind of homecoming.
Come for late morning, walk the shaded side of the streets, and save the ramparts for the last hour of light, when the stone gives back the day's heat and the whole town comes up onto the walls to watch the sun go down past the lighthouse.