Came here while visiting Donostia and we managed to get free entry! It's a really great museum and…read moreit's manageable for spending as little as an hour, unless you want to go through all of the exhibits in substantial detail, which could take quite a bit more time. There's a lot of old Basque history including seafaring history, whaling stuff, and then more modern stuff, too, ranging from Basque artists to, I don't know, secret Basque space lasers. The architectural integration of the old cathedral and cloister is also well done-- leaving the sanctuary, you walk out into this gorgeous, peaceful grassy area and aren't even thinking about the fact that the upstairs is more of a proper museum setting. Definitely worth a visit

Definitely recommend visiting if you are in San Sebastian for more than a couple of days, or if…read moreit's raining and are looking for an indoor activity. It's a great way to learn about Basque history and culture and it includes a church and cloister as part of the building's structure. Bonus: they have a a cafe with tasty pintxos and tapas for the appetite you will work up walking through the museum.