Lisbon
Tiled hills, cheap seafood, and the best sunset spots in Western Europe. Stay 3–5 days, or 5–7 with sintra and the coast.
The travel-industry consensus best month: warm seas, thinning crowds, dropping prices, and everything still open.
September holds summer sea temperatures with spring crowd levels around the Mediterranean. The single best month for island-hopping.
Three thousand years of layers, and the best carbonara within a mile of anywhere. Stay 3–4 days.