A working Catholic cathedral inside the old city walls, founded by Spanish Franciscans in 1716 and rebuilt several times since. The current building is late 19th century, with a single bell tower and a plain whitewashed interior. It is the seat of the Catholic Archdiocese of Xi'an and serves an active local congregation — Mass is in Mandarin, with a Latin sung Mass on selected feast days.
Worth a short detour if you happen to be in the western half of the walled city. Open most days outside service times.