Arabat Fortress
Lenine Raion of Crimea, Ukraine · built 1700
The Arabat Fortress, built in the 17th century by the Ottoman army, stands at the southernmost part of the Arabat Spit. Its purpose was to guard the spit and Crimea from invasions. It was in use, with intermissions, until the Crimean War of 1853–1856.
Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).