Cetatea Enisala

The village of Enisala (Turkish: Yeni Sala, Bulgarian: Ново село, "New Village") is the site of a fortress dominating nearby lakes (previously gulfs) of Razelm and Babadag. Dated to the late 13th or the beginning of the 14th century, it was built to control the travel routes that passed through the region. The fortress' three hexagonal tower are the only of this type found in the whole region of Dobruja.

http://en.wikipedia.org/wiki/Enisala