San Lorenzo stands on the north side of Piazza IV Novembre, across from the Fontana Maggiore and adjacent to the Palazzo dei Priori. It is Perugia's cathedral and the city's most prominent medieval church — and, unlike many Italian cathedrals, it has a deliberately unfinished facade. The exterior is built of pink-and-white marble in a striped Gothic pattern on the side facing the piazza, but the main facade was never completed and remains bare stone. In a city that spent so much on art and architecture, this permanent incompleteness is oddly characteristic.
Inside, the cathedral is richly decorated despite the exterior austerity. The Chapel of the Holy Ring (Cappella del Santo Anello) holds a relic claimed to be the wedding ring of the Virgin Mary — a claim that has attracted pilgrims since the 15th century, when a group of Perugians stole it from a church in Chiusi. The ring is kept in a box with 15 locks, each with a different key held by a different official.