Located in the mouth of the Ría de Vigo, the Cíes Islands protect the bay from the harsh Atlantic climate.
It is a group of three islands, Monte Agudo to the North, Faro, and San Martiño to the South, plus a number of small isles: Agoeira, Penela dos Viños, Garabelos and Ruzo. Their coasts are varied, alternating sandy beaches with cliffs and coves.
Their highlights are the Rodas Beach, which serves as a bridge between the islands of Monteagudo and Faro, and the Lake of Nenos, a shelter and hatchery for young fish and for a number of aquatic animals. The most abundant animal species in this natural park are seagull and cormorant, but other fowl like goshawk, pilgrim falcon and crow are also present. Mammals like rabbit, hedgehog and a few individuals of male feral goat thrive there as well. The submarine bottoms are covered by the calcareous seaweed Lithothamnion forming the so-called Maërl bottoms. Numerous colonies of barnacle and mussel coexist on the cliffs and rocks with fields of sea anemone and individuals of sea urchin, and with plaice, turbot, sole and bivalve mollusks on the vast underwater sandy areas.
Humans have lived on the Cíes Islands since the Palaeolithic period. The hill fort of Castro das Hortas, from the Bronze age, is the first known construction. There are also traces of Roman settlements and of religious buildings belonging to the Middle Ages, such as the Monastery of Santo Estevo on Faro and the Hermitage on the Southern Island. In the 19th century several buildings were erected, including the garrison of the Carabineros do Reino, one prison and two salt processing plants. The Cíes were inhabited until the mid 20th century.
On October 17th, 1980 the Cíes Islands got the Natural Park status, and on June 13th, 2002 the Spanish Parliament passed legislation to establish the Land and Marine National Park of the Atlantic Islands, which includes the Cíes Islands and extends further North to the islands of Ons in the Bay of Pontevedra, and Sálvora and Cortegada in the Bay of Arousa. Since 1988 these islands have been recognized as a special protection area for fowl and are part of the European Natura Network 2000. Underwater fishing is banned since 1992.