This map in PDF can be downloaded here.
The tower of the castle (Château de Dinan), although the castle itself is not very picturesque.
It makes sense to visit a high stone viaduct over river Rance, built in the mid 19th century, which offers beautiful views of the old port of Dinan.
The official title of Dinan is a city of art and history. Therefore, in addition to numerous museums, there are various installations on every corner.
There is a Clock Tower of the 15th century in the center of the old town with an observation deck. Unfortunately, the view from above is not picturesque as the roofs of Dinan are all gray.
Also we walked through the park Jardin des Petits Diables, where located a mini-zoo.
Getting there: by train (http://www.sncf.com/). If you have a car, then find few big parking lots in the center. From Saint-Malo the best way is to take a bus 10 (http://www.tibus.fr/, schedule)