The monument of Nikolaos Sialmas is at the southernmost tip of Agios Efstratios.

The monument was erected in memory of the heroic Air Force Lieutenant Nikolaos Sialmas, who lost his life defending the Greek airspace. The Mirage aircraft of the heroic Greek man crashed in an area south of Agios Efstratios on June 18, 1992.

To commemorate his sacrifice, this memorial was built at Tripiti, the southern cape of Agios Efstratios, which has since been renamed to Cape Nikolaos Sialmas.

The monument is visible from a great height and carries the famous dictum of Leonidas " Molon lave ", a phrase that since antiquity inspires and exemplifies all Greeks who defend their country. It also features a shield and a spear which are the emblem of the unit in which the heroic lieutenant belonged.