You don't appear to be able to get into the castle, but it is next to the church and there are wonderful views from the grounds.
This coffee shop was where our "guide" dropped us off for a cup of coffee or tea, and a biscuit before we explored the town. They have a good selection of spanish pastries and biscuits which you can eat there, or take away. After your stroll around the local tourist attractions you can kill time waiting for the coach to return, with a coffee and pastry you can sit outside and peruse the car park (with the semi-ruined cathedral in the background) while you ponder why one of the local souvenir shops has decide to branch out with an "Adult toys" section...
Favorite Dish: Cake, Biscuits, Pastries, Biscuits, Pastries and more Cake. Oh, and a coffee.
This bar, in the Calle de Belen, can't be missed as the entrance is a submarine's door. Inside is a small seating area, with some interesting decoration (I seem to remember there being DVD covers on the wall), and pretty loud rock music playing!
Castro is a small fishing village that has grown and become a commuter town for Bilbao and Santander. Additionally it attracts many visitors for its beauty and excellent food.
As a result, traffic can be bad, and parking difficult.