Mystery photo challenge: Where in the world is this port?

Editor's note:

(CNN) -- Can you guess where this is? Write your answers at the bottom in the comments section. We will announce the answer Monday on the Mainsail page.

Hint 1: This harbor's name refers to 'obsidian glass'

Hint 2: The harbor belongs to this country's biggest city, but it isn't the country's capital.

Hint 3: The body of water is 70 square miles (180 square kilometers).