Here in this chapter Hugo informs us that in addition to the convent itself and the boarding school there was a third building that was known as “the little convent” on the grounds of Petit-Picpus. This little convent was a house that lodged nuns from various different orders, providing them with a refuge of sorts. These nuns obviously had different practices, and none were anywhere near as strict as the rule practiced by the sisters that actually made up the main convent at Petit-Picpus.
Hugo also lets us know in this chapter that the public DID have access to the chapel on the grounds, but it was constructed in a way that the public could never see the sisters and the sisters could never see the public.