Bajamar, a coastal town about 3 km from Tejina, has a complex of sea water swimming pools; two large ones and a children's pool, with showers and changing rooms.
Entrance is free, you just pay a small charge for the other services.
Near the pools there is a small sand beach next to the breakwater, and a path along the coast from here.
Playa del Arenal is between Bajamar and Punta del Hidalgo. It has black sand or pebbles, depending on the time of year and the tides.
There is a walkway from the old Hotel Neptuno, on the main road, right down to the beach.