[Galadriel55]

The reason I ruled out a lot of places is 1) has to be where Morgoth's spies wouldn't see him - what keeps them from checking out all the other random lumps of rock? Nothing much, really; and 2) Turgon has to be close enough to be relevant. I mean sure, he could have even gone over the Ered Luin, but then he's less in the picture and less worrisome. He can't get into the play in time to change events; he has to be physically present on site to make a difference that would affect Morgoth.

(Again what no one realized is that Gondolin's importance was in making Earendil and not in their strength at all, but then no one has the same reader's knowledge as us, so they all assume that the way of defeating Morgoth must be through battle with him and through survival when battle is not possible).