Kanli Kula Fortress (Turkish for "Bloody Tower") is an open-air amphitheater built by the Turks in 1539 and used as a prison until the 19th century.

Not much to do inside but it is a nice spot for views of HN and Bay of Kotor from above.

In summer, there are concerts at sunrise, follow their event list on the website.

Entrance is 8 euros per person which is somewhat expensive but if you don't have a car to drive to other fortresses in the area (or if short on time and can't hike to other fortresses), this one is a good pick where to go.