Make tracks to Fort LEcluse and learn about its role in defending against attacks and invasions. This structure has witnessed some interesting history during its time.
You're spoiled for sightseeing choice when in Leaz. Fort L'Ecluse is an ideal place to kick off here, but there are lots of other interesting attractions to visit. Bellegarde Canyon, Pertes de la Valserine, and Jeanne d'Arc Theatre are near the history-filled fortress and will fill in your day nicely.