The "seven streets" of the "old town" of Bilbao are rather dead in the daytime although it is interesting to walk down them and look at the details of the old buildings. The area seems even gloomier if you are passing through on a typical rainy afternoon. They are virtually pedestrian streets, although you should watch out for the occasional passing vehicle.
The energy level picks up well after sunset, as the locals go cruising by the various bars in this area. This is a good area to just pick a place that strikes your fancy, order a txacoli (tart white wine) and pick some pintxos (bar snacks, like tapas) to munch on. I know, I cannot pronounce these Basque words either, but my Castillian Spanish seemed to work for me in a pinch in Bilbao.
This area of glorified alleyways is centrally located just east of the river.