3 days covers Lisbon itself, or 2 city days plus Sintra, not both

Plan A day 1: the castle, then down through Alfama to the river

Day 2: Belém, a sit-down pastel de nata, the tower from outside

Day 3: funicular up to São Pedro de Alcântara, then down to Baixa

Plan B: Sintra on day 3, two palaces, timed tickets booked ahead

Rain: move Belém to the wet day; the Jerónimos cloister is covered

An airport base loses an hour a day; both plans are in the guide