Originally Posted by Jugni

I know that lines are taken from Grecian Urn and there is no explicit escape at all but for me his imagination is some sort of escape.
In the very opening stanza Keats gives us a contrast between something unchanging ( the urn) because it is dead and something transient because it is alive. At the beginning he enjoys this permanence and immortal love but soon this permanence and immortal love brings frustration and negation because it lacks life. So in the final stanza he concludes that real beauty lies in truth (reality), not in art (imagination).
I am again saying that according to my humble opinion, meaning of "truth is not this world but acceptance of this world means "reality".