Snoopy, Come Home (1972)

Charlie Brown's (Chad Webber) beloved dog Snoopy (Bill Melendez) receives a letter from his original owner, Lila (Johanna Baer), who has been sick in the hospital. With his bird friend Woodstock, Snoopy goes to visit Lila, making his way across the country despite seeing "no dogs allowed" signs everywhere. When Lila gets better, she asks Snoopy to live with her. After a farewell party, he sets out to live with Lila, leaving Charlie Brown depressed.