The island of Kyra Panagia is sometimes also called Pelagos or Pelagonisos. It is de name of the largest deserted island north of Alonissos. It is 25 km2 in size and its highest point is 299 meters. The island is mostly covered in low shrubs and vegetation, but there are also some olive trees. In ancient times the island was known as Ephthyros and as Polyaigos. Administratively Kyra Panagia is part of the municipality of Alonnisos, but the island belongs to the Megisti Lavra Monastery on Mount Athos, since it was given to them by the Byzantine emperor in 963. Nowadays there are people that rent the land from the monastery to graze their goats. Because there are many springs on the island it is a good place to keep animals. There is a monastery on the east side of Kyra Panagia which is currently (2011) under restoration. It is inhabited by a single monk.

Kyra Panagia has two natural harbours, Agios Petros and Planitis. The last one, Planitis, is the safest of the two and like many harbours on the Greek islands this used to be a shelter for pirates during the Middle Ages. Excavations of ruins in the bay of Agios Petros opposite the islet of Melissa, have shown that it has been inhabited since the Neolithic times, in about 6,000 B.C. Ceramics, small statues, tools and animal bones have been found. It is believed that Kyra Panagia was the site of ancient Alonissos. Close to the island, in the bay of Agios Petros, a shipwreck has been found of a commercial vessel that carried 3,000 to 4,000 wine amphorae.

On the eastern side of the island lies the monastery of Kyra Panagia from which the island derives its name. It was built in 1100 A.D. in the shape of a small fortress (this was done as a protection against attacks from pirates). Close to this monastery lie the remains of another much older Basilica. Kyra Panagia is open to visitors.