Poblado de Guinea, tubo volcánico and Lagartario is a wildlife-oriented stop with obvious family appeal, but it can also be worthwhile for adults who want a change from streets and museums. The best visits are unhurried, with time to watch rather than simply move from enclosure to enclosure. It is a little away from the tight centre, but still close enough to fold into a half-day plan if the subject interests you.
Look up feeding times, conservation notes, and seasonal hours before setting out. If you are sensitive to animal attractions, read recent visitor information first; standards and the feel of the place can vary, and it is worth knowing what kind of experience you are choosing.