Château de la Bâtiaz
The Château de la Bâtiaz is a short walk from downtown Martigny. It was built in 1260 and is the only remaining witness to the medieval era. It was an object of envy, and passed from the House of Savoie to the Sion bishops (and vice versa) many times.
It is a nice hike to the top and a great spot for a picnic in nice weather.