Lemnos is an island of Greece

Greece

Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

 in the northern part of the Aegean Sea

Aegean Sea

The Aegean Sea[p] is an elongated embayment of the Mediterranean Sea located between the southern Balkan and Anatolian peninsulas, i.e., between the mainlands of Greece and Turkey. In the north, it is connected to the Marmara Sea and Black Sea by the Dardanelles and Bosporus...

. Administratively the island forms a separate municipality within the Lemnos peripheral unit

Lemnos (peripheral unit)

Lemnos is one of the regional units of Greece. It is part of the region of North Aegean. The regional unit covers the islands of Lemnos, Agios Efstratios and a few smaller, uninhabited islands, in the Aegean Sea.-Administration:...

, which is part of the North Aegean Periphery

Peripheries of Greece

The current official regional administrative divisions of Greece were instituted in 1987. Although best translated into English as "regions", the transcription peripheries is sometimes used, perhaps to distinguish them from the traditional regions which they replaced. The English word 'periphery'...

. The principal town of the island and seat of the municipality is Myrina

Myrina, Greece

Myrina is a former municipality on the island of Lemnos, North Aegean, Greece. Since the 2011 local government reform it is part of the municipality Lemnos, of which it is a municipal unit. It covers the west coast of the island, and has a land area of 82.049 km², about 17.2% of the island's...

. At 477 km², it is the 8th largest island of Greece.
Lemnos is mostly flat (hence its more than 30 sand beaches), but the west, and especially the northwest part, is rough and mountainous (highest elevation: Mount Vigla, 470 m).