First, you will need the ability to lay an egg. Once you've progressed in the story far enough to defeat Zope and Cactuardo, you'll be able to pass the construction workers at the top of the shaft in Infierno. At the top of the next shaft and before entering Isla Bonita, go right and through a tan block to enter a chicken dungeon. Battle your way to the bottom to unlock the power to lay an egg by pressing
. If you haven't received it yet, you can also get another achievement at this point by pressing
12x:
Now, head to Isla Bonita and make your way to the save point above the Olmec head. Slide down the column on the left and Wall Fly left from near Flame Face to land near a house on the far side. Enter this house and speak to the chicken who will tell you to lay an egg. Do so and the achievement will pop. You will now also be able to enter Tule Treetops Top to get a piece of the Golden Key as well.