Most of Baixa is younger than it looks. The 1755 earthquake flattened the medieval downtown, and the Marquês de Pombal rebuilt it from nothing on a dead-straight grid — Europe's first great planned, quake-resistant city centre. This walk reads that grid from the river up.
Two and a half kilometres, best in the afternoon when the light comes off the Tejo into the square. Start at Praça do Comércio, the arcaded river square where the royal palace stood until the wave took it. Through the Arco da Rua Augusta — climb it for the view straight up the grid — and onto pedestrian Rua Augusta, where every cross-street was set to one plan.
Off to the left, the Elevador de Santa Justa, the 1902 iron lift to the Carmo ruins above. Then Rossio, the old heart of the city, paved in the wave-pattern calçada that makes the ground seem to ripple. Sit; watch it work on everyone who crosses.
End one block over at Praça da Figueira, the castle framed above the roofs, the metro below, and a small glass of ginjinha (cherry liqueur) from the corner counter to finish.
