Just below the castle stands the small church of São Pedro, the oldest surviving building in Leiria. The Romanesque portal with its concentric arches dates to the late twelfth century, when the church served the medieval village clustered on the slope beneath the castle walls.
Most of the rest of the structure has been rebuilt over the centuries, but the original carved tympanum and one Romanesque side door survive. The interior is small and unadorned; it takes ten minutes to see properly but the doorway alone is worth the short detour off the path up to the castle.