Puerta del Carmen is one of the few surviving pieces of Zaragoza's old defensive walls, standing in the middle of a busy traffic junction west of the historic centre. The gate dates from the late 18th century and has the sturdy, slightly battered look of a monument that has watched the city grow around it.
It is not a long visit, but it is a good orientation point if you are walking between the Aljaferia side of town and the central streets. The stonework still carries the memory of the sieges of Zaragoza during the Peninsular War, which gives this small gateway more weight than its size suggests.