The Canal du Midi at Port Saint-Sauveur

Pierre-Paul Riquet's canal opened in 1681 to link Toulouse to the Mediterranean, and it still runs right through the city. At Port Saint-Sauveur it widens into a basin where barges are moored permanently, ten minutes on foot from the busiest streets and a world quieter.

The towpath is the frame: a long straight tunnel of plane trees with the water flat below, dappled light on the gravel and boats to lead the eye. Bridges every few hundred metres give a raised viewpoint and a stone arch to shoot through, and the basin itself gives colour and reflections.

It works from mid-morning to evening because the canopy softens everything overhead, which makes it a useful plan B when the open squares are too harsh. In autumn the leaves go yellow and drop into the water; note that plane trees along the canal are being replaced in places because of disease, so a stretch that was fully shaded a few years ago may now be open.