The Evil Chicken's Lair is entered through a teleport by using a raw chicken on the Chicken Shrine northeast of the Fairy ring entrance of Zanaris (an undead raw chicken will not work, there are two chickens around the shrine which can be killed and used on it).
It is accessible during and after the Recipe for Disaster: Sir Amik Varze subquest during which players must kill the level 271 Evil Chicken (or 179 if the player's combat level is under 91). Players should note that to access the Evil Chicken's Lair, they must have spoken to the Wise Old Man in Draynor Village.