If you were thinking of something to do to start your day, finish your day, or waste your day away in Autumn, Tokiwa Park is your best bet.
A short distance from the city centre (about 10 minutes on foot), and a short walk from all the major city hotels, this park is perfect for a tranquil walk, or jog, and a fantastic place to park yourself and read a book.
The colors are simply amazing, boats are available for hire, and the Art Museum sits quietly at the southern end of the park. In the next few weeks the colours will disappear to make way for the "whiteout" that is the Asahikawa winter, so if you're in town now, or the next few weeks, cruise down to Tokiwa Park for some quiet time.
Note also that during the winter, most of the paths are cleared of snow allowing you to negotiate your way through the park with easy. Just make sure you have some good winter gear with you.