The Papal Apartments are a strong contrast to the dungeons, both open to the public, where philosopher and monk Giordano Bruno and sculptor-goldsmith Benvenuto Cellini were once imprisoned.
Giordano Bruno and Benvenuto Cellini were held prisoner in The Papal Apartments. 
mnli hypothesis: Giordano Bruno and Benvenuto Cellini were held prisoner in The Papal Apartments.  premise: The Papal Apartments are a strong contrast to the dungeons, both open to the public, where philosopher and monk Giordano Bruno and sculptor-goldsmith Benvenuto Cellini were once imprisoned.