La Rochelle is home to three famous towers. Tour St-Nicolas, on the east side of the mouth of the harbour, is the most architecturally interesting, with two spiral staircases that intertwine but never meet. On the opposite bank is Tour de la Chaine, which houses an exhibition on seventeenth-century emigration to French Canada. You can climb along the old city walls to the third tower, just behind Tour de la Chaine, known as the Tour de la Lanterne, or Tour des Quatre Sergents – after four sergeants imprisoned and executed for defying the Restoration monarchy in 1822. All three towers have fine views back to the port, and the entry ticket includes a trip on the electric ferry (passeur), which tirelessly crosses the water all day.