Barberini Palace: great anthology of Italian Art.

Beatrice Cenci (attributed to Guido Reni)

This glorious gallery is a must! 
Especially after the recent refurbishing.
Built for the pope Urban VIII, the Palace's project is by Maderno, Borromini and Bernini.
See the amazing staircases by Bernini (square) and Borromini (oval).
The Salon ceiling is decorated by Pietro da Cortona (Triumph of the Divine Providence trompe-l'oeil fresco).  The collection is stunning:  a show of the major and most important Italian paintings of all times,
arranged in order to provide an overview of the development of Italian art.  Masterpieces include La Fornarina by Raphael, The Annunciation by Filippo Lippi,  Guido Reni's Beatrice Cenci, Hans Holbein's famous portrait of Henry VIII. For Caravaggio fans the gruesome Judith beheading Holophernes and Narcissus. Hopefully the wonderful gardens will be restored very soon.