Kız Kulesi (Maiden's Tower or Leander's Tower) at the southern entrance of the Bosphorus Strait, Istanbul.
The tower is built on a small islet which is believed to have supported some kind of structure since the early 5th Century. The present stone structure replaced a wooden one that was burnt down in 1721, when it also began to be used as a lighthouse.

Since 1994 the tower belongs to the Turkish Naval Forces Command and in the late 1990s it underwent an extensive restoration & then rented to a private facility for tourist purposes.

At some point the lighthouse function was transferred to the small white structure at right in the photo, as the Kiz Kulesi Lighthouse is described in https://www.suustunde.com/en/content-details/istanbul-strait-lighthouses.html?ContentID=145 as having “a height of 9 m and a focal plane of 11 m; red or white flashes every 3 seconds (position). 41 ° 1’15.92” N, 29 ° 0’15.28” E”..
See also https://en.wikipedia.org/wiki/Maiden%27s_Tower & https://muze.gen.tr/muze-detay/kizkulesi for detailed history