Easily mistaken for an ornate church spire, the conical 15th-century Tour de la Lanterne is La Rochelle's beauty queen. It was so named because of its role as the harbour's lighthouse (lit by an enormous candle) and is one of the oldest of its kind in the world. It is sometimes referred to as Tour des Quatre Sergents in memory of four local sergeants, two of whom were held here for plotting to overthrow the newly reinstated monarchy before their execution in Paris in 1822.
From the 17th to 19th centuries, the robust cream-stone tower was a prison. Prisoners exercised on the 158 stone steps that spiral up to the lantern, from where stunning city views can be enjoyed today. On the way catch your breath on five different floors: some walls are decorated with nautical or militaristic pictures and English-language graffiti carved by English privateers held here during the 18th century. Don't miss the backgammon board carved in the 19th century by a prisoner into the wooden floorboards in room No 4.