The King Naresuan Shrine and Wang Chan Palace Ruin is located across the Nan River from Wat Phra Si Rattana Mahathat, on what used to be the grounds of a large school. The school has been closed and is being demolished so that the foundations of the old Wang Chan Palace can be slowly uncovered and studied.
King Naresuan was born in the Palace in 1555, and the grounds now have a small shrine which contains a life-sized statue of the King pouring water out of a cup to symbolise a declaration of independence from Burma. This shrine is very popular with the locals, who burn incense and leave offerings at the foot of the statue. There is also a small museum here with pictures and legends of the King's life. Some English captions are available, so it's definitely worth a browse.