Well, a good place to start is looking at the first stanza of this excellent poem and seeing the number of metaphors that are contained even in the first three lines. Let us remember that a metaphor is an example of figurative language that compares one thing with something else without the word "like" or "as." See if you can spot the three metaphors in the first three lines of this excellent poem:
Thou still unravished bride of quietness,
Thou foster child of silence and slow time,
Sylvan historian, who canst thus express
A flowery tale more sweetly than our rhyme...
The speaker of this poem then begins his Ode by comparing the Grecian urn he is contemplating to an "unravished bride," a "foster child of silence and slow time," and a "Sylvan historian." Note the point of these metaphors: Keats is highlighting how the urn is undamaged by time by comparing it to a virgin bride; he is saying how it has long been protected by comparing it to a "foster child" of time and silence"; and lastly, he shows how it preserves history by calling it a "Sylvan historian." Now, see if you can find any other examples of literary devices in this poem. Good luck!