Wat Chang Rop is the outer-zone ruin most likely to stay with you. Its large bell-shaped chedi stands on a high base decorated with dozens of elephant figures, many of them worn down but still powerful.
The temple sits in the forested Aranyik area north of the old city, so it feels removed from the town even though it is easy to reach by bicycle. Go here for the best sense of Kamphaeng Phet's rough laterite style.