Playa de Arnao, Sandy beach in Arnáu, Spain

Playa de Arnao is a shell-shaped beach in the village of Arnao, Castrillón, about 300 to 350 metres long, with fine whitish sand and a small stretch of rounded pebbles, backed by vegetation and a few scattered houses. A 500-metre seafront promenade links it to a multi-kilometre green trail. Its moderate to strong waves make it a surfing spot, and near the beach lies the Arnao platform, fossil coral reef layers.

Arnao beach lies beside the old Real Compañía Asturiana de Minas works, the mining company that shaped the village of Arnao in Castrillón. The beach's identity is tied to that industrial past rather than to a restored headframe, which the sources do not mention. Nearby, the Arnao platform exposes fossil coral reef formations in three rock layers: limestone, shale-marl, and red and green marls.

The beach shares its name with Playa de Arnao in Figueras, in the council of Castropol, so the two are often confused. Nearby stands the old Real Compañía Asturiana de Minas, whose presence ties the cove to the mining history of Arnao. In summer two beach bars open on the sand, and the L-1 bus line (La Luz–Piedras Blancas) stops close by.

Access is via the N-634, taking the turn-off towards Salinas past a tunnel and the El Cuerno and El Dólar beaches. A car park, an L-1 bus stop (La Luz–Piedras Blancas) and two summer-only beach bars sit near the sand. Showers, toilets, water fountains and bins are on site, with lifeguards on duty in summer.

Near the beach lies the Arnao platform, a fossil coral reef with three distinct rock layers: a limestone set, a slate-marl set, and a set of red and green marls. The beach shares its name with another Arnao beach in Figueras, in the council of Castropol.