Porto Cathedral

The Sé do Porto crowns the hill where the city started, and it looks the part: begun in the 1100s as much fortress as church, its twin crenellated towers built to survive sieges as well as praise God. Prince Henry the Navigator was baptised here; João I married his English queen Philippa here in 1387, sealing the Anglo-Portuguese alliance that is still, seven centuries on, the world's oldest active treaty — a fact Porto, whose port trade ran on English money, has never stopped enjoying.

The interior keeps its Romanesque gravity — a narrow nave of heavy granite — with baroque outbreaks where the 18th century got in: the silver altarpiece of the Blessed Sacrament chapel (legend says it was plastered over to hide it from Napoleon's troops, who marched past without a glance) and Nicolau Nasoni's loggia stuck to the north flank like a rococo apology. The paid ticket buys the cloisters, and they're the reason to pay: Gothic arcades wrapped floor to vault in blue-and-white azulejo scenes, a staircase by Nasoni, and the upper gallery's view over the terracotta cascade of the Barredo down to the river.

The cathedral terrace outside is free and underrated: the whole lower city, the Douro and Gaia's lodges in one sweep, with the morning light behind you. Come at 9 when it opens — the terrace to yourself, the cloisters before the tour groups — then walk DOWN through the medieval alleys of the Barredo to the Ribeira, the direction gravity and history both intend. Twenty minutes away, São Bento station's 20,000-tile hall is the natural next stop; the two make Porto's best free-ish morning.