If you've played Zombies in "Call of Duty: Black Ops," you're probably aware that each of the recent Zombie maps has a hidden quest which requires an insane number of secret steps to complete. The latest Zombies map, "Shangri La," is no different, and if you're interested in unlocking the Time Travel Will Tell achievement for a cool 75G, you're going to want to follow a walkthrough to show you all the steps. Seriously, follow a walkthrough. Once you watch the video below, you'll realize that you could never figure this stuff out on your own. Unless you work at Treyarch, that is.
For tips on mastering the other maps, check out our "Call of Duty: Black Ops" Zombies Mode survival guide.
NTGAchievements did an excellent job compiling the process into the following steps (with included shortcuts to that part of the video):
Watch the video just to know what you're looking for and the, while you're playing through, it's a good idea to have a text guide handy. Look no further than the "Call of Duty" Wikia, which proves to be a great resource.