You could spend a month of Sundays exploring the city of Oaxaca  and still have plenty left over. However, in about four fairly relaxed days, you can take in most of the downtown highlights.
Start out with a leisurely day of people-watching and café-lounging around the invitingly tranquil old zócalo. For activity, explore the nearby Palacio de Gobierno , the colorful Mercado Juárez , the exquisitely baroque Iglesia y Ex-Convento de San Agustín , and the Catedral de Oaxaca  with its mysteriously intriguing Santa Cruz de Huatulco .
Spend your second day relaxing along the Andador de Macedonio Alcalá  pedestrian mall, checking out the many fine handicrafts shops, the Museo de Arte Contemporaneo , and the Ex-Convento de Santa Catalina , now restored as the Hotel Camino Real. Be sure to enjoy lunch on the relaxingly cool patios of the Danzantes or Hostería Alcalá restaurants.
Highlight your downtown exploration with at least a day around the Centro Cultural de Santo Domingo , which includes a pair of unmissable stops: the world-class Museo de las Culturas de Oaxaca, and Oaxaca’s pride, the radiantly lovely Iglesia y Ex-Convento de Santo Domingo.
Spend your fourth day following your own interests, such as investigating more handicrafts stores, especially MARO  (Mujeres Artesanís de los Regiones de Oaxaca); visiting small museums, notably, the Casa de Juárez  and the Museo Prehispanico de Rufino Tamayo ; or more sights, such as the intimate Arquitos and San Felipe del Agua  village neighborhoods or the gemlike Basilica de Nuestra Señora de la Soledad  and adjacent museum, Museo de la Soledad.