Hey folks

I've never been to Mexico, but have traveled extensively in both the developed and developing worlds. I'm looking for a short trip to clear my head, like 3-4 days. I'm based in SF, and so I figured this would be a good opportunity to experience Mexico for the first time. But given that it's a big country with many places that are easy to get to, I'm a bit stumped on where to start. I like a place where I can a feeling for the real place - not a resort type of town. My ideal is to wander around streets, markets, and neighborhoods, experiencing a bit of local life, eating street food, practicing my Spanish, and spending relatively little money.

A friend recommended Guanajuato. I found reasonable airfare with a good itinerary. Does it fit the bill for a good spot to visit for 3 days to do the types of things I like? If so, what part of town should I stay in? Any recommendations for things to do, places to stay, food to eat? Will I be bored? Are there things to see nearby? If it's not a great first-time-in-Mexico destination, what other places would be good?

Also, how easy is it to get to and from the airport, especially in early morning?

Thanks in advance!