Chiang Mai was built in 1296 as a walled city surrounded by a moat. The old city was roughly 1.5km square. Whilst a good portion of the original city wall has collapsed the four corner bastions are still intact along with various other sections. The original moat is still in use to this day. Chiang Mai city is basically made up now of the old city (within the walled area) and the new city which has grown up around it. Grab a Tuk-Tuk and go for a scenic visit to Chiang Mai's lovely moat and the ancient walls of the old city.
If you like ancient temples (Wats) and buildings, then visit Chiang Mai and the surrounding areas, they are full of them, several hundred in fact. A good number of these ancient temples are still in use today by the Buddhist monks.