Go to the bus stop across from Mercado Hidalgo and take a bus for 5 pesos that says "Camion Central", it takes about 15 minutes to get to the main bus station. From there you can get to just about anywhere in the area on 1st or 2nd class buses. A 2nd class ticket to Leon costs 40 pesos and a 1st class is only 49. The 2nd class bus takes about 45 minutes and comes every 20 minutes. A bus to San Miguel is 75 pesos and the trip was about 1 1/2 hours.
Guanajuato downtown is a fairly small place, so it is easy to reach most of the touristic attractions simply by walking, you won't spend one dime, it is much healthier and that way you'll be able to enjoy all the small streets that are very nice to visit.
Walking here has the advantage that, thinking about the preservation of the heritage, many areas are exclusive for pedestrians, so using a car may be more a nuisance than an advantage. if you have your hotel in downtown then your only problem will be buying a good map in a touristic information post to help you navigate, if you are a bit far away then just take a taxi to aproach you there and walk during your visits.
Guanajuato has many tunnels and the streets are narrow and ,many are blocked to traffic. Many others are long one way roads and it is a nightmare for the tourist to drive there. We drove but we parked at the hotel and took a cab for our stay.
A good intro to the city is to park up on at the Monumento al Pipila, take in the grand view of the city, and then head down into town via the Funicular. The cost is 20 Pesos (about $1.85 USD) per person for a roundtrip up and down the hill. You get wonderful panoramic views on the way up and down. The Funicular takes you to the back of the Teatro Juarez, in the heart of the downtown area, where you can began exploring the city by foot.
If you park up at the Monumento, it wouldn't hurt to buy one of the small information booklets sold by local vendors. The book is about 30-50 pesos, and is chock full of stunning pictures and information about the city's sites and history.
Normally I would have thought it would be better to take a plane from Mexico City to Guanajuato (or Leon), but my friend thought we should take the bus. She was right. The bus ride was 5 hours, but it was the most comforatble busI have ever been on (even in Canada), they gave you a packaged snack, and even had televisions on it! Best of all, it was much cheaper than flying.
The river was diverted underground and the riverbed is what you see here. Above, are the parks, homes, schools and businesses of Guanajuato. Because of this underground road, traffic is much more bearable in the streets. If you visit by car, the best parking is with the hotels that are on the roads coming in.
The best way to know Guanajuato is walking arround. Having car there is difficult coz a lot of streets are close, actually almost all of the downtown's streets are just for walking.
You can leave your car in one of the parking lots. They charge you about $0.7 dlls for each hour, but is best you can do.