Oaxaca-4 days, and no plans yet

Since you know nothing about Oaxaca, or Mexico . . . why did you choose this trip?

Well, you are in for a treat. Not to blow off your request for info, but I urge you to get a good travel guide and pore over it. With only four days, you'll want to make sure you get to see the things that most interest you. With a little homework, you'll be able to hit quite a few high points. For instance, you might wish to see Monte Alban early in the morning, hit the Abastos market on your return (where you can also get a meal), freshen & rest up at your hotel, then back out to explore downtown. That might include a visit to the women's cooperative on 5 de Mayo, a stroll up Alcala, then a restorative coffee in the zocalo. That would be one day, without exhausting yourself. Here's a website that might interest you: Oaxaca tourism.
You'll be fine here as a female alone. Obviously, use the same good judgment you'd use anywhere. Your good Spanish will be a boon. This is a pretty small city, and easy to maneuver on foot. Colectivos leave from Abastos (where the 2nd class bus station is also located) to all the surrounding villages, and there are some smaller bus line depots dotted around south of the zocalo that go out of town.

I liked the Hotel Victoria up on the hill. Great swimming pool and an open-air bar overlooking the city. Food used to be pretty good too. Go down to the Zocalo, check out the cathedral, take tours to Mitla and Monte Alban (don't miss), and look for the giant tree they call El Tule - can't remember where it is.

If there for a sunday dont miss the market at Tlacolula, about 20 miles east of town. Used to get the bus from next to the baseball stadium, up from the ADO bus station. For me of all the markets to visit this is the one.

Monte Alban of course.

Dont miss the museum contained within the old convent, adjacent to Santo Domingo. There is a fabulous 'garden' attached to it and I would guess that American botanist still does those excellent early morning guided tours. Just pop along to the entrance on that corner to sign up.

DO NOT MISS an opportunity to visit monte alban. busses leave from the hotel rivera del angel. people watch and eat elote on the zocalo, get your hands on mezcal to wash down some chapulines (grasshoppers--they taste like sun dried tomatoes). MARO is an excellent artisan cooperative that supports female artists in oaxaca state (5 de mayo) and casa de las artesanias de oaxaca (matamoros 105) is lovely as well. on the south side, i remember a big market (its mercado 20 de noviembre, bw 20 de nov and cabrera) where there were tons of food stalls with authentic oaxacan food. try a oaxacan tamale wrapped in banana leaves or chicken mole. grab a churro or some spicy peanuts on your way out.
enjoy!

I'm with No. 2 on the wisdom of getting a guidebook. The Moon one on Oaxaca is pretty good, for instance. That way, in combination with the suggestions here, you can make decisions on how to spend your time. You say that you would like to get out of the city one day. In addition to the suggestions above, San Martin and the village where they make and sell black pottery are two good choices. With some knowledge of spanish you are in a good position to navigate local transportation. I agree on magnificent Monte Alban and the more subtle Mitla as must-see ruins. If you've been searching this forum, you probably came across the Oaxaca Calendar site which was posted by someone (sorry, can't remember whom to give credit); there may be something special happening during the time of your stay. Have a good trip! Wish I could be in Oaxaca for four days about now.

On the 17th, 18th and 19th the local baseball team - the Guerreros - is playing and is good fun. A dollar for a bottle of Corona amidst the warm air - they bring it to you - and its a little slice of local life. I'm a Brit and it was great fun!! The stadium is just up the main road of Ninos Heroes from the ADO bus station.

Ah those grasshoppers... Vegetarian apparently and you may find the smaller ones easier to digest (pun intended). No shortage of mezcal shops to try the stuff - gratis of course.