1. Basilica of San Petronio
The Basilica of San Petronio is the largest church in the city and sits right on Piazza Maggiore. Construction began in 1390, but the facade was never finished, which is why the top half is still rough brick while the bottom has white and red marble. It was originally intended to be larger than St. Peter's in Rome, but the Pope stopped the project to build the Archiginnasio instead.
Inside, the church is massive and feels very open compared to other cathedrals. You can find the world's longest indoor meridian line, which was designed by Gian Domenico Cassini in 1655. It is 67 meters long and still works perfectly today when the sun shines through a hole in the roof. There are also 22 side chapels with various artworks and religious relics. The church is a key part of the landscape and one of the main Bologna attractions.
Entrance to the main part of the basilica is free, but there is a 2 Euro fee if you want to take photos. You can also visit the terrace for a small price to get a view of the city center. Be careful about your clothing as they have a strict dress code for visitors. The unfinished look of the exterior makes it a unique part of the skyline that people often stop to photograph.