Hi – I was thinking southern France – Provence, around Mont Ventoux, and the towns of Malaucene, Bedoin. I have a house there, and the cycling is sublime. Haute Route do a 3 day event there (I did that in 2017), as well as Ventouxman (I did also in 2017) and the annual Ventoux half marathon (hurty – did that in 2019 – 21km up with average gradient of 8%).
I think there is the opportunity to do a triathlon camp, with focus on bike. There is a large lake for open Water swim practice ( lac du Paty).
Best weather is probably June or September. There are multiple excellent bike shops to rent bikes if required. Nearest airport is Marseille about 1.5hrs drive away. Boutique hotels and upscale hotels all over the place. Spectacular scenery includes Mont Ventoux, Gorge du Nesque and the Dentelles de Montmirail (Google has some pretty pictures). Plus lots of Vineyards of the Gigondas, Cotes du Rhône and AOC Ventoux.
If you are interested I can pull a few rides together from my cycling log and Strava. Happy to help etc. it would be fun.
Gareth