You don't have to be religious to appreciate the calming atmosphere of Arctic Cathedral. Ask when the next mass starts or when it's open for general viewing.
If you're spending a while in Tromsø, Arctic Cathedral is a good place to kick off your sightseeing. This principal church is one of numerous attractions worth checking out here. Tromso Lapland, Tromso Cathedral, and Polaria are also waiting to be explored nearby.