What is the route to eternal happiness?
Being at peace with oneself is the route to happiness. When our minds are not running after material goals but instead being comfortable in the current and now, that's what leads to sustained happiness. Else one is running after temporal happiness, which come in the form of something that satisfies us in the moment but us not sustaining - e.g. watching TV or eating good food. Eternal happiness comes from the state of mind and not from achieving a goal we are conditioned towards