A bit off the regularly traveled i.e. downtown path, but worth a visit.
If possible go more than once. In daylight to get oriented.
If only once, go at night. The illuminated Basilica outside and inside is spectacular at night. The architecture and decor of the cathedral (built 1690 to 1730) is inspiring.
Whatever your religious beliefs, if attending on a sunday, or at the time of another evening mass, the devotion of the local congregation will be very moving.