We were in Bilbao last August. We stayed at the Hesperia Hotel. It's across the river (estuary?) from the downtown business center- and there is a pedestrian bridge within a couple of blocks. The Guggenheim Museum is probably 1/2 mile away. This was in conjunction with a river cruise in Bordeaux. Next stop was San Sebastian. Great trip, but Bilbao was a good 'base', but not a highlight itself. Don't miss a side trip to Guernica.
Loved the Basque country, the people, the pinxtos, the txakoli wine. The 'tx or xt' sounds like 'ch'.
You didn't ask, but I liked San Sebastian a lot more. Bilbao is a spread-out industrial city. San Sebastian/Donostia (in Basque) is the place the Spanish royal family go when Madrid is too hot/cold for them. It's much more compact, and for 'foodies', it has the highest concentration of Michelin starred restaurants in the world.
Jim