Have you ever seen an old film with Marcello Mastroiani (don't remember the title, something with 'amore') situated in old Pavia? The same streets and houses are here till now. And the same cobblestone streets - gives pain to your feet if your shoes has a thin sole...
The Crypt of St.Eusebio is located in Piazza Leonardo da Vinci. Apart the ruins there isn't nothing to see!
The area of Pavia is a habitat of many birds, like the cormorants who like to relax in the waters of river Ticino just beneath the Ponte Coperto bridge.
A Sunday walk near the Navigli zone can be a nice idea. If you're lucky you will see some nutria that live in the waters of canal.