The Santiago Cathedral lies at the hearty of the casco viejo's narrow streets. Originally dating from the 13th century the tower and facade are more recent. From here the original 'seven streets' of early Bilbao lead down to the river. Bilbao is one of those places where it is easy to see how the city has expanded from the early small settlement by the river - the area around the cathedral can't have changed much in many hundreds of years and retains it's individual character from the rest of Bilbao. Having said that, don't think that casco viejo is now a backwater or tourist area - it is still as busy as ever packed with shops, bars, cafes and is home to many Bilboans. It's also virtually traffic-free which makes eating outside much more pleasant. Try and get a hotel in this quarter - although it won't be luxurious it's much better than a modern block in the new town.