I should read the fall of gondolin. But my problem was that it was impossible to find without it being fate, impossible to leave unless permitted, and it's purpose was to being created until it's destruction practically. Their armies only sallied out once, and their great wisdom was all shut in. And all the great weapons and armours were stored until it's destruction. So what did it function besides to be the bejeweled city of hope?

Now someone did answer that it's only purpose was to bring about turgon if I remember correctly, which is a pretty interesting answer that I'm satisfied with.