Complex sentence: Inmates who were deemed dangerous or disturbing were chained, but Bethlem was an otherwise open building for its inhabitants to roam around its confines and possibly throughout the general neighborhood in which the hospital was situated.
Split into simpler sentences: Inmates who were deemed dangerous or disturbing were chained, but Bethlem was an otherwise open building. Its inhabitants could roam around its confines and possibly throughout the general neighborhood in which the hospital was situated.