One of your first stops should be Tourism Office of the Ploërmel Community: Josselin Site. Here, you'll be able to find your bearings and get some great tips before you begin exploring.
To explore this tourist information center, make tracks to Josselin. You'll find loads of other worthwhile attractions in the area, like Josselin Chateau, Basilique Notre-Dame-du-Roncier, and Musee de Poupees.