This astonishing aqueduct, striding towards the monastery from the northwest, was built between 1593 and 1613 to supply water to thirsty monks. Its 180 arches, some of which are double-decker, are thought to have been designed by Filippo Terzi. It’s best seen just off the Leiria road, 2.3km from town, where it winds along a dramatic turn. You are free to climb about the top at will.