Ktenia (Bulgarian: Ктения, Greek: Κτένια) is a ruined Roman and medieval fortress, 2.1 kilometres (1.3 mi) north of the village of Lozarevo in Sungurlare Municipality, Burgas Province, south-eastern Bulgaria.

The ruins of the fortress lie northeast of the town of Sungurlare, in the Grebenets section of the Eastern Balkan Mountains.

In ancient and medieval times, it served as an important defensive position guarding the Karnobat Pass through the mountains.

It is uncertain whether Ktenia is identical with the castle named Goloe, which lay in the same region, or whether these were separate fortifications.

However, it was lost during the period of uncertainty after the premature death of his son George II Terter (r.