Half an hour by train from Milan, Pavia is a small but interesting city on Ticino river.
The main points of interest are:
The Covered Bridge, the Cathedral, Saint Peter Basilica with the white marble Ark, the Visconteo Castle and medieval churches, towers and gates that populate the centre.
Courtesy of: Konki at it.wikipedia (CC BY-SA 4.0.)
In the northern neighborhood, reachable directly by train, the imposing Chartreuse stands out, a monumental sanctuary in gothic style
https://www.certosadipavia.it/cathedral/
Courtesy of: Blackcat at it.wikipedia (CC BY-SA 4.0.)