Grand Canal in Venice, Italy

The road that runs on water. Grand Canal in Venice, Italy

What if a city's busiest street had no road? In Venice, Italy, traffic flows along the Grand Canal, a 2.4-mile waterway that winds through the city in a giant reverse S-shape. Known to locals as the Canalazzo, it is Venice's main water-traffic corridor, carrying vaporetti, water taxis, gondolas, police boats and other vessels. The canal follows the course of an ancient river that once flowed into the Venetian Lagoon.

Nearly 170 historic buildings line its banks, many built by wealthy Venetian families between the 13th and 18th centuries. With palaces and houses rising directly from the water, the Grand Canal has little room for conventional pavements.

Despite its importance, only four bridges cross it: Rialto, Scalzi, Constitution and Accademia. For centuries, boats were the main way to cross. Today, a journey along the canal offers a moving look at Venice's architecture and history. Here, even a traffic jam comes with a view—and a gondolier.