Santa Maria of Sasso Sanctuary is a holy place where religious souls gather to pray. You can do the same, or respectfully observe others as they worship.
You'll have sightseeing choices galore when staying in Bibbiena. Santa Maria of Sasso Sanctuary is a good place to start here, but there are loads of other fine sights to experience. Sanctuary of La Verna, ExpArt, and Poppi Castle are not far from the sacred place and and will cap off your day nicely.