Castillon and the Col de Castillon are on the mythical Route de Grandes Alpes, on the route from Menton to Sospel and Moulinet
Route des Grandes Alpes Departure : Thonon-les-Bains - Arrival : Menton
Variants are available on
https://www.francevelotourisme.com/itineraire/route-des-grandes-alpes-r-a-velo
Variants are available on
https://www.francevelotourisme.com/itineraire/route-des-grandes-alpes-r-a-velo