This sprawling botanical garden inside the massive walls of the Ex-Convento de Santo Domingo was the first of its kind in the Americas. Many plants that are now known throughout the region were first cultivated here. Species found only in Oaxaca are on display, including many varieties of cactus. Two-hour-long English-language tours are conducted on Tuesday, Thursday, and Saturday at 11 am. There are daily Spanish-language tours. You must take a tour to gain admission, and tours fill up quickly, so sign up as early as you can. Afterward you can roam the grounds.