You can explore the area using the map here.
To take a close up look at the interior of the Basilica, along with a commentary. If you have Google Cardboard, you can use the image to view the Basilica. Play the soundcloud file for a commentary on the interior.
Go inside and head for the Sistine Chapel. Have a look around using this fantastic interactive tour.
All that is left is the choice of dining venue for the evening before you head to the opera to watch Tosca (set in three locations you have visited in your first two days in Rome - Basilica Sant'Andrea della Valle, Palazzo Farnese and Castel Sant'Angelo).