Park on the D5 at the marked parking space near the kilometer post
number 30. This is not far south of the junction of the D5 with the
D2 at Thorenc. Your route to the cache heads up the mountain along
an old Roman way.
Castellaras is the ruins of a fortified place (oppidum) perched
at 1,400m - a chapel, a small palace and a few houses, all
surrounded by the village walls. It's a fascinating place to
explore; but even better, bring a picnic and eat it looking out
over the amazing views.
Note on cache maintenance: I'm now living in
Vence, which is about 45 km away from this cache.