St. Ignatius Cathedral is the great Catholic landmark of Xujiahui, with twin spires, red brick walls, and a Gothic Revival interior that feels quite different from Shanghai's temples and shikumen lanes. It is a useful stop if you are exploring the west side of the former French Concession.
The cathedral is active, so visits are best kept quiet and respectful. Dress modestly and avoid turning up in beachwear or slippers, as staff can be strict about entry.