Bilbao is the capitol of this area and houses the Guggenheim museum. The building is designed by Frank Gehry, who also designed the Weisman Art Museum in Minneapolis, MN. I am not a huge fan of modern art, but if you have an educated and informed tour guide, they can make the art come alive. It displays the new age of art, using natural materials, structures, and technology. The Puppy by Jeff Koons is my favorite, made all the more attractive with the spring flowers.
San Sebastian is on the Bay of Biscay and is a quaint beach city where you can wile away the hours just watching the tides go in and out. A nice relaxing stop between tourist sites.