The Oratory of San Bartolomeo is considered the oldest surviving religious structure in the Arnasco commune, predating the parish church of the Assunta and likely serving an early medieval community in one of the valley hamlets. Small, plainly built, and easy to walk past, it is worth seeking out for the sense of continuity it provides — generations of Arnaschesi attending services in the same low-ceilinged room before the village grew and acquired its more ambitious church.
The oratory is modest enough that you may need to ask locally for its exact location, which is part of its character. It is not signposted as a sight, which is true of most things worth finding in Arnasco.