(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).