Great place to spend a week. Monte Alban is worth a visit. It's been a few years since I was there, but I remember taking a day trip to visit several small towns in the surrounding countryside known for their different textiles and food.
The market! Get lost wandering around. Watch them mix mole' paste and discover more things than you ever knew existed. The food is spectacular as well. It's a beautiful city. You can also go outside the city to villages where they make incredible handicrafts. Have fun!
Have fun. Just got back from a quick trip a couple of weeks ago. Catedral was our favorite meal (dinner). Also ate at El Destilado (i think that was the name)really cool little place with a 9 course meal w/ drink pairings. Very reasonably priced and the owner comes out to your table to explain each course/drink.