Plaza La Marina is on the right about midway down avenida Castilla Perez as you head towards Torrecilla beach.
The plaza has several very good bars and restaurants (Taperia La Plaza, Pata Negra, Sol y Mar, Teteria Karabeo and La Marina), all of which have terraces of varying sizes.
La Marina is an excellent fish restaurant and a great tapas bar. In the summer, it tends to get absolutely packed and you can often end up waiting for a table.
The square itself has a good, safe play area for kids, which is an advantage if you are eating at one of the restaurants and they get a bit restless, as kids do!