Neptune. Epic fail lol. Seriously though I beleive the the traveler is the key. I think the garden that is being referenced inside the traveler is the black garden. It being pure light surely the twist is that it also embodies the darkness. The story I think will be locking the traveler into the light or dark but we being the way we are will destroy the traveler with untold effects. Interested to know if the vex are the true beings off darkness or not.