The Secret Zoo, sometimes referred to as the "Hidden Zoo" or "Forgotten Zoo," is an additional smaller zoo space separate from the main zoo, featuring it's own main building. Players can visit the secret zoo via the Main Building Menu in their main zoo or by clicking a signpost located in the lower-right corner of the main zoo. The Secret Zoo becomes accessible after the main zoo has been expanded three times. This can be done by achieving level 30, or by buying the expansions with Zoo Dollars.
The secret zoo has it's own attractiveness score, and therefore the number of people it draws and the amount of pet pennies it earns are separate from the main zoo. While this is the case, the pet pennies, zoo dollars, and pawprints earned in the secret zoo are pooled with those earned by the main zoo.
The secret zoo starts out at 56 plots and can be expanded 13 times by spending tools or zoo dollars. While the secret zoo is not unlocked until after the third zoo expansion takes place, tools can be earned at any stage of the game and are only used for this purpose. It is often the case that when players unlock the secret zoo, they already possess enough tools to expand it at least once.