One of my favorite things to do in Busan is to ride a small boat at Taejongdae (태종대). The ride doesn’t take more than an hour, but it’s so much fun on a clear day. We went at the end of September and saw dolphins last time.
I recommend exiting Nampo-dong Station (남포역), exit 6. Then, take local city bus #8, #30, #88, or #101, and get off at Taejongdae Terminal. This is approximately a 30 minute ride.
Keep your eyes open for any signs stating “Taejongdae Gonpo Cruise Boat.”