Marvel at the size of Truro Cathedral. Fit in a mass if you can or simply take a seat and appreciate a break from the outside world.
You're spoiled for sightseeing choice when staying in Truro. Truro Cathedral is a good place to kick off here, but there are plenty of other worthy spots to consider. Hall for Cornwall, Pendower Beach, and Trelissick Gardens are not far from the principal church and and will cap off your day nicely.