Pictures at an Exhibition
Pictures at an Exhibition describes someone walking round the exhibition and looking at the pictures.  The ten pictures he describes in music were drawings and watercolours.  Mussorgsky starts his piece with a tune which describes the person walking round the exhibition.  It is usually known as the “promenade” theme (a promenade is a walk).   At first Mussorgsky puts the promenade theme between each picture, but he does not do that all the way through the piece.  Some of the later pictures have bits of the promenade theme in the music.