The Lost Thing by Shaun Tan

A curious boy discovers a strange, oversized creature wandering unnoticed in a drab, bureaucratic city and feels compelled to help it find where it belongs. After meeting indifference and hitting dead ends, he follows a cryptic clue to a hidden realm where the creature finally fits, and he quietly lets it go. Later, he reflects on how easily people stop noticing odd, wonderful things once they grow up.