23 is a work written in 1886 - 87 by the Belgian composer César Franck for solo piano.
As the name implies, it comprises three movements: a prelude, an aria, and a final.
With the tempo indication as Allegro moderato e maetoso, 4/4 (common) times, it begins with a half march-like character, with tension slowly building up and the flow of the music increasing.
The mood of this slow movement is fantasy-like, gradually turning into a chorale with tension building up and the increasing music flowing progressing much like the first movement.
The restless character finally becomes gentle, fading away into a last tonic chord in ppp.