There are dozens of travel agencies scattered around Oaxaca City, and all offer guided trips to outlying archaeological sites and villages. Always available are half- and full-day tours of the city, half-day excursions to Monte Albán, and full-day journeys to Mitla. You can also book trips to villages that coincide with market days. Note that if you enjoy scenic drives and generally taking your time, you'll be happier renting a car or hiring a taxi as packaged tours don't give you much time at the ruins nor the opportunity to spend time wandering from workshop to workshop at the crafts villages.