Hakodate is a city in the south of Hokkaido and was originally a port which eventually flourished into a thriving city location. It is overlooked by Mount Hakodate which is accessible by cable car but can also be hiked or reached by car. The view of the city from the summit is breathtaking and is especially picturesque at night. There is also an old fort called Goryokaku; although the arsenal and a well is all that remains of it. There is a festival in mid May which reenacts the time when the fort was built.
The fish markets in Hakodate are within a few minutes walk from JR Hakodate station. Be sure to try the salmon roe while you are there!