Some small islands like As Freitosas and O Xubenco surround the main isles of Ons and Onsa. The Isle of Ons has always been inhabited and its people lived of commercial relations with Bueu and Pontevedra. In the 1970s the "illans" emigrated to the peninsula of Morrazo, leaving the Isle practically deserted, except during the summer months, when a high amount of tourists come in the ferry from Bueu and San Xenxo. 

The Isles' highest point, Alto do Cucorno, holds the lighthouse of Ons. Following the path to the North there are the birds' reserve, the impressive Mount Centolo and the beautiful Melide beach. 

The Celtic village of Castro do Alto is situated in the South as well as the beaches of Pereiro and Os Cans, where there is an anthropomorphic grave known as "A Laxe do Crego", which can be observed in low tides. The lsle of Onsa can be seen from O Fedorento, and at O Alto cliffs there is the spectacular "Burato do Inferno", the Hole of Hell. 
 

Ornithological reserve 

The priviliged location of the Ons, in the entrance of the Pontevedra and Aldan's creeks, converts the Isles in a very rich habitat. There are bird colonies like the Phalacrocorax artistotelis (600 couples) and Larus cachinnans (4000 couples). Apart from the bird migratory species there are also a large amount of rabbits, very easy to watch at night time. 

The Atlantic waters of Ons and Cies enjoy a great richness and biodiversity, and mammals like the Delphinus delphis or the Tursiops truncatus can be seen from the Isle.