San Quirico d'Orcia has been a waypoint on the Via Francigena — the great medieval pilgrimage route from Canterbury to Rome — since at least the 12th century. The town sits at a natural stopping point where the route crosses the Orcia river, and the Collegiata was built in part to serve the thousands of pilgrims who passed through each year.
You can still walk sections of the Via Francigena through the Val d'Orcia. The route is well-marked with white-and-red blazes, and the stretch between San Quirico, Bagno Vignoni, and Radicofani is the most scenic. Allow a full day to walk the Bagno Vignoni to San Quirico section (about 12 kilometres), and book accommodation in advance — the pilgrim hostels along the route fill up in spring and autumn.