I don't think any even medium sized city of renown in Europe can be seen in less than two days and usually more is needed. Depending, or course, on what one's interests are. To know and experience a new place, it's not just going to the better known sights but also wandering around, seeing the people, sampling the local food, and the rest. Bilbao is special as one of the larger (largest?) cities in Spain's Basque area. I enjoyed seeing the unique inside and outside architecture and layout of the Bilbao Guggenheim much more than any of the art I saw inside. I was also a bit disappointed that it's a pretty small museum. Personal taste is involved and we're all different. There's much more in Bilbao than just this museum.

DH took this a few years back. the leaves almost look like a prop, they were so vibrant!

Carmelita's first snows - before and after grooming pics.

It was a phrase I first heard from a fellow I worked with from India...somehow I picked it up as it's a way of saying your otherwise occupied without having to get into the details as to what you're doing instead.