This image beautifully depicts the concept of purgatory.  The person standing in the foreground is a symbol of a soul wandering between two worlds.  The tall red mountains in the background, along with the big red moon, represent the unknown and perhaps frightening borders of purgatory.  The sky changing from darkness to light can symbolize the transition from life to death or from sin to purity.

 Birds in flight are symbols of other spirits that wander in this in-between space.  Leafless trees and rocky ground reinforce the sense of barrenness and expectation.  This image well shows the feeling of loneliness, reflection and maybe even the hope of liberation in Purgatory.