El Charco del Ingenio is a large botanical garden and nature reserve just outside the dense center, covering about 67 hectares of protected land.
It’s especially known for Mexican cacti and other succulents, including rare and threatened species, and combines a botanical garden with a canyon, wetlands, wildlife, and walking trails.
It’s open every day from 9am to 5pm. Entry is about 100 pesos, and kids under 10 get in free.
It’s on the edge of town, about a 35-minute walk from the Centro and uphill nearly the whole way, so a bus or car is probably a good idea, at least for the way up.