I've visited several of the belfry sites from 2009 to 2017.
Each of the various belfries is usually the tallest structure in each town, built for defensive and civic purposes. Contrary to what most people might think, the belfries were mostly secular, with only a few of the structures being associated with churches.
Visiting any of the individual belfries isn't that hard, as it is just a matter of going to the particular town where the belfry is located. Getting to all 55 would just be a matter of determination.