Dyo Aderfia (meaning Two Brothers) are two small rocky islands, at a distance of 5,8 n.miles from Patitiri (port) southernly of Alonissos. They have only one small beach named Ostria, located at the estern side of the big island, facing Gaidares rocky islets. The two islands are separated from each other from a narrow band of sea and their area is very good for fishing. The bigger one reaches in height the 178 metres and small 154 metres. They do not have anything interesting (besides the nice sea water that is found all over the area) to offer however a visiti there it is a nice trip for those who like adventure and virgin destinations.

Small bushesand other plants adapted in the rocky ground cover their surface. In both islands live many poisonous snakes!

In the region come often also the diving schools of Alonissos for educational dives as the underwater surface is very interesting.

As the Peristera island, Dio Aderfia belong in Area B of National Park, where do not exist concrete rules of protection.