Yes secrets are back in destiny and one of the first one is solving how to open the golden chest that is within the lighthouse. Here is the video on where you can locate all the books to unlock the chest.
https://youtu.be/ZpnO-GUOh_c
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It's not really secret, plus it is a region chest just like all of the other region chests in the game. You can see those symbols on the map and that's where the chests are located... Hell there are two more region chests on the east and west sides of mercury but there's no way to get to the spot where they're at. So I'm confused on how you're supposed to get those 2 chests, and I want the 6 tokens that I'm going to get for opening them...