The most venerable building in Porvoo is its cathedral, the oldest parts of which date from the late 1200s. Some visitors refer to it as "the unluckiest building in Finland." Ravaged, rebuilt, and plundered repeatedly during its tormented life by, among others, the Danes and the Russians, and damaged by aerial bombardment in August 1941, it became a cathedral in 1723 when Porvoo was defined as an administrative headquarters for the local church.

Tragedies within this building continued in ways that seemed relentless. On the night of May 29, 2006, the cathedral was ravaged by fire, which was started as a deliberate act of vandalism that was widely condemned throughout Scandinavia. As of this writing, because of the fire, all ceremonies within the cathedral had been canceled. The fire did not cause much damage to the actual structure of the church because the ceiling did not collapse. However, the church was badly damaged by smoke and water. Some windows were broken and chandeliers fell down. Repair works have started, but local authorities estimate that it will be several years, at least, before the church's interior can be visited once again by members of the general public.

For the purposes of getting a better understanding of Porvoo, however, the church stands prominently on what looks like a verdant country lane in the town center, surrounded by antique stone and clapboard houses. As such, the church is often sought out by day-trippers from Helsinki as a symbol of the sufferings of Finland itself.