How does Bologna celebrate Saint Catherine's feast day?

Because it is the name of the town where she was in the convent and died.

In Lent of 1463, Catherine became seriously ill, and she died on March 9th. Buried without a coffin, her body was exhumed eighteen days later because of cures attributed to her and also because of the sweet scent coming from her grave. Her body was found to be incorrupt and remains so today in the Church of the Poor Clare convent in Bologna. She was canonized in 1712.