The central feature of the Casino is the Ballroom, which is a full two storeys high. Caretti maintained the architectural structure he inherited from Valadier but added two structures for musicians at the sides and lined every part of the room with paintings, stuccoes, marbles and gilding.
The vault is decorated with stories of Eros, frescoed by Domenico Toietti and Leonardo Massabò, and the lunettes contain the Flight of the twelve hours, the Flight of the Three Graces (both by Massabò) and Parnassus by Francesco Coghetti.
The two orchestra structures stand on superb grooved columns made of Carrara marble, decorated with ornate capitals and architraves adorned with white stucco and gilt cupids by Pietro Galli.
The walls are lined with stucco imitating ancient yellow marble.
The floor used to have a large polychrome copy of the Palestrina mosaic, but this was removed in 1888 and taken to Palazzo Torlonia in Piazza Scossacavalli, and is today replaced by a polychrome marble floor.