Tour Solidor is a 14th-century tower at the mouth of the Rance estuary in the Saint-Servan district, about 2km from the Intra-Muros. Built in 1382 to control shipping entering the Rance, it is one of the few medieval structures in the area that predates the corsair city. It now houses a small museum dedicated to the history of Cape Horn voyages — Saint-Malo was a major departure point for the southern seas, and many of its sailors rounded Cape Horn on voyages to the Pacific.
The tower is best reached by walking south along the Rance estuary from the old town — a pleasant 20-minute walk. From the top, the view takes in the Rance estuary, the tidal power station downstream, and the Dinard coast across the water. The museum inside is specific and interesting, especially for anyone with a taste for maritime exploration.