You needn't be religious to enjoy the calming atmosphere of Museo Diocesano Chiostro dei Canonici di San Lorenzo. Ask when the next mass starts or when it's open for general viewing.
You'll have sightseeing choices galore when spending time in Genoa Historical Centre. Museo Diocesano Chiostro dei Canonici di San Lorenzo is a great place to start here, but there are loads of other worthy spots to experience. Aquarium of Genoa, Piazza de Ferrari, and Luigi Ferraris Stadium are not far from the principal church and will top off your day nicely.