Reading the other reviews, it is obvious that casual visitors do not understand the program. You can walk the grounds and there is a small museum with limited hours, but there is a very special FREE TOUR at 10AM SHARP. You enter the main building and go to the far end and wait in front of an iron gate. At 10AM, a monk opens the gate, lets in about 50 people, and then locks the gate. The tour of the facility and monk living quarters is about an hour and extremely interesting, although it is offered only in Italian language. There is no fee, but everyone gave the guide a tip of about 5 euro, and he asks visitors to buy things in the gift shop to support the institution, which I did. Please buy there and not from the unrelated vendors out on the street in front of the complex. There is a nice, inexpensive book in English that explains the history, and you can study after your tour.

Well worth the trip, the Certosa is magnificent, particularly its marbled facade. I didn’t make it to the the 10am tour so looked around self guided. Entrance to the main building is free. A monk beckoned us to pass through the metal gates inside & discover the stunning chapels hidden within, & then onward to the interior courtyards. A donation is expected upon departure, with most following the lead of €10. The rule not to take photographs was widely, if furtively, ignored. Didn’t appear to be strict adherence to modest clothing particularly either. There is car parking close by & the attraction is served by bus & train. The latter takes 7 or 8 minutes from Pavia. There’s a bit of a walk from Certosa Station to the monastery, around a kilometre. The museum was closed during my visit, but a little shop selling honey & such like was open.

An extraordinary complex starting in the 14th century with additions over several centuries. The tombs of several Visconti dukes of Milan are there, one of great complexity. Try to visit the museum, where casts of the individual tomb panels and figures on the facade are easier to study. Very different architecture to the contemporary work in Florence, less marble, and a lot of ceramics and terra cotta. The monks are still there, and you can buy their products such as honey and liqueurs. For students of the monastic life also go and look at the Certosa di Calci, near Pisa. Check opening hours.