Impressive! The vertical photos give a good idea of how the castle towers above the valley. I've been in the Briançon region twice for a cycling holiday, but not in the Queyras - it's really in the middle of nowhere.
Have you ever visited Forte Bramafam across the border in Bardonecchia? I just noticed it on the map and I'm making a note for myself too. It's a military museum with plenty of 20th century artillery.
I have been to the hill fort of Mont-Dauphin at the lower end of the Guil. You could easily walk around an hour or two there, with great views of the mountains around the Durance valley. The fort includes a village with restaurants and still has room left for a park where a regiment could practice marching. But I guess that wouldn't be as interesting for the boys as actual guns.
I'm not familiar with either fort you mention. I'll keep both in mind for if we ever go there again. Congrats for climbing those cols on bike. I'll never be able to do that. Hiking is easy. Biking is impossible for me...
Posted using Dapplr