The Parc National de la Vanoise (wvanoise.com) occupies the eastern end of the Vanoise Massif. It’s extremely popular, with over 500km of marked paths, including the GR5, GR55 and GTA (Grande Traversée des Alpes), and numerous refuges along the trails. For in-depth information on the various routes, head for the tourist offices in Val d’Isère, Bourg-St-Maurice and Méribel.
To cross the park, you can take the GR55 from the Lac de Tignes and over the Col de la Vanoise. You can then connect with the GR5, which brings you out at the southern end of the park in the town of Modane. There are countless shorter but equally beautiful walks in the park. Settlements in the Arc Valley, like Bessans, are good bases to start exploring the park, but even the ski resorts of Tignes, Val d’Isère and Méribel are good starting points.