The Certosa di Pavia is one of the most important buildings from the Italian Renaissance period and it has a good collection of art work.
It's possible to visit the monastery. Opening hours (May 2008) are 9:00 Tuesday - Sunday and closing for lunch from 11:30 - 14:30. Closing hours in the evening vary depending on the season. (check this page for current information - in Italian) It's possible to get to Certosa by train or bus from Pavia or Milan.
The Hotel Italia (book direct) is 800 meters away and there's a bus stop in front of the hotel with buses running to Milan and Pavia.