An image of The Sacred Golden Link
The Sacred Golden Link is a hidden easter egg within The Game that can be found by always clicking on the first option when prompted until reaching the Game Over screen at which point you have to scroll down to the bottom of the page. There you will find The Sacred Golden Link (which also links to this page).
The Sacred Golden Link is also not the only "hidden link" within the game. As the Ascension Ending also requires for you to find links hidden in a similar manner to The Sacred Golden Link.