You'll probably see St. Stephens Cathedral in the skyline before you actually find this incredible place of worship. Look around inside if it's open or just appreciate the facade from the street.
You'll have no end of sightseeing choices in Brisbane Central Business District. St. Stephens Cathedral is a great place to begin here, but there are plenty of other interesting spots to discover. Suncorp Stadium, Roma Street Parkland, and The Gabba are not far from the principal church and will fill in your day nicely.