The Spyder easter eggs were the most prominent easter eggs in Riven. Actually, there are several different easter eggs (five known so far), all unlocked with the same rather complicated and time consuming procedure. Essentially, the player will need to click through a series of hotspots, spread both in time and space throughout the game. There are also certain hotspots that one must not click.
Clues to find the hotspots to click were released by Spyder. There was, however, no official word on how to trigger the actual eggs; only how to unlock them. The rest was up to fans to discover by themselves.