The easiest way to unlock this achievement is to do so in "La Mansión del Presidente."
The "Nooks and Crannies" achievement consists of you finding all of the secrets of a single area (in other words getting a 100% in an area).
Go to "La Mansión del Presidenete." Once you are there, there will be a platform over which there is a treasure chest that, once broken, contains money for you. Since this is the only secret in "La Mansión del Presidenete," you will effectively have discovered 100% of the secrets in the area and therefore unlock the "Nooks and Crannies" achievement!
It takes about five seconds to unlock this achievement once you visit "La Mansión del Presidenete."