Nothing beats spending time by the water. Gather the troops, throw together a picnic and get some fresh air at Praia de Arnela.
You're spoiled for sightseeing choice when staying in A Coruña. Praia de Arnela is a great place to kick off here, but there are many other worthy sights to visit. Cape Finisterre, Cape Finisterre Lighthouse, and Praia do Rostro are near the stretch of coastline and and will cap off your day nicely.