The Rhone valley between Villeneuve and Martigny has some terrific places to ride because it's still largely agricultural and it's criss crossed with public paths and tracks. There are several stables around Noville, Aigle and Bex with direct access to fields and tracks. Probably too far from Lausanne (30 mins car ride) to do everyday but for a chance to blow the cobwebs away with a good long trot/canter it's the best.