By Sharon Otasowie, Associate Editor A fragile treasure built on 118 islands off Italy’s northeast coast, it’s a miracle that Venice has managed to survive and thrive for more than 1,000 years. The city has built a naval and commercial empire and created an immense collection of palaces and churches, full of priceless paintings, to which an estimated 20 million tourists flock to every year. With the plan of an underwater fortress of steel designed to rise from the depths during high tides to protect the lagoon city of Venice, it’s among the most ambitious works of civil engineering in modern Italian history. But decades after the idea’s formation, Venice remains…