Bilbao to San Sebastian

You do not need advance tickets for the museum and aside from the art collection, the interior design is nothing to look at compared to the exterior. I think 3 1/2 hours is enough and I would buy bus tickets 2-4 weeks in advance depending on when you are traveling there, which makes a difference.

We visited in October 2013, arriving in Bilbao by train from Madrid, stopping at the Guggenheim, then picking up a rental car for driving to San Sebastián and surrounding area. After several nights in San Sebastián, we returned the car in Bilbao and stayed one night in the old quarter.

Walking to view the exterior of the museum can take some time. The old quarter was enjoyable - I’d recommend taking a taxi there from the museum, and spending some time to see it if this is your one time in Bilbao.

Be sure to see the exterior of the Guggenheim from as many angles as possible. There's a walkway along the water with some sculptures as well as different views of the museum.

Check what's showing at the Guggenheim before buying a ticket; most of it is rotating exhibits rather than a permanent collection. I disagree that the interior isn't of interest, however - in places, it's quite disorienting due to the unusual way the rooms are connected.

The old town of Bilbao is large and very interesting, with lots of unusual non-chain stores - well worth wandering around (I liked it much more than San Sebastian's old town). The Ribera Market has a few good pintxo stands on the ground floor (good for lunch or dinner and open every day) as well as lots and lots of stands selling fish and meat, and just a few selling produce, open Monday through Saturday.

The Bilbao funicular is OK, but if you're going to San Sebastian, the view from their funicular is far more spectacular. On a short visit, the Bilbao funicular is not a priority.

Not on your list, but two places in Bilbao that I found very worthwhile. The Bellas Artes Museum has lots of great stuff (if you like the Prado, you'll like this one). And the Museum of Artistic Reproductions has exact replicas (plaster casts) of many famous sculptures; it's like going to the Louvre, the Vatican, the Pergamon, and others, all in one small-ish, inexpensive, and easy to see place.

I'd go for the 7-1/2 hours in Bilbao. I liked it much better than San Sebastian, whose historic center is a lot smaller and massively touristy.

Thank you for all the great feedback. I just discovered that there are other bus services lurraldebus and Pesa that leave every 30 min or so from Bilbao to San Sebastian giving us more freedom in how much time we spend there. Any comments on the bus services?

Sorry, we traveled northern Spain strictly by rental car and train, not bus. But a bus every 30 minutes sounds really convenient, not having to wait around the depot for a long time, or killing a lot of your day waiting for the next bus. Must work for commuting locals!