The Route du Temps is a signed route that winds through some of the area's most dramatic valleys, historical sites and rock formations; it starts just north of Sisteron and follows the D3 to St-Geniez, up and over Col de Font-Belle (1304m) to the medieval fortified village of Thoard.
Interpretive panels along the way explain what you're seeing, and if you fancy a closer look, various trails criss-cross their way into the surrounding hills. It's also worth stopping in Thoard for a visit to the Distillerie du Siron, a small-scale organic lavender factory run by local maker Marc Malagutti.
In total, it's a journey of around two to three hours, depending on how many stops you make. For further information and a route map (€2), contact the Sisteron tourist office.