Porvoo Cathedral is the most important medieval building in Finland, a grey stone church on the ridge above the old town that has stood in some form since the 13th century. The current building is largely 15th-century Gothic, though it has been rebuilt and expanded after two fires. The white-painted interior is typically Lutheran — spare and light — with a few fragments of medieval frescoes surviving.
The Cathedral's hilltop position gives it visibility from most of the old town, and the climb up from the riverside offers good views over the wooden houses and the river below. The churchyard surrounding it contains graves dating back centuries and is worth wandering on its own.