We camped at Igueldo Camping only a few k's from the center, taking the bus No.16 from outside the campsite which made it easy to explore the center of the old city and walking all the way along the bay to the far end, where you can hop on off the bus.
The lovely bay de la Chonca
Sardines. You can find fish restaurants along the far side of the port.
Pintxos bars found on every street in the center, good way to try different pintxos and local wines