Montreal began on a triangle of land where a small river met the St Lawrence, and the cleverest museum in the city is built directly on top of it. Pointe-à-Callière is both the founding spot of 1642 and an excavation you walk through underground — the rare history museum that is the history it describes.
Start there, below ground, among the first foundations and a stone-vaulted Victorian sewer, then come up into Place Royale, the city's first marketplace, and the old Custom House on its edge. Walk Place D'Youville west, the long square laid over the buried Saint-Pierre river, past the obelisk to the founders and the old red-and-grey fire station.
Cross to the Old Port and the river that explains everything — the quays, the 1922 Clock Tower you can climb for the harbour. Then back up cobbled Rue Saint-Paul, the oldest street, its warehouses now galleries, to Place Jacques-Cartier and the carved doors of Notre-Dame. The metro at Place-d'Armes takes you out, four centuries later.