Island Sant’Andrea. Sant'Andrea is a small island in the Venetian Lagoon, nothern Italy. It houses the fort of Saint Andrew (Forte di Sant'Andrea), a large fortress built in the 16th century to defend Venice. It is one of the islands of the Venetian lagoon I visited. Cruising to the fort one can be impressed by the imposing construction but it is only when you get inside, that you can have a strange physical feeling of total emptiness and mystery.