EDIT: I was reading up on it on the Council of Elrond, and the description just seemed perfect for our guild:
Council of Elrond
Turgon was aiming to prepare a last refuge against foretold disaster, but yet he also wanted to dwell in a fair place, as much like Tirion as possible. He found the location for Gondolin after being told by Ulmo to go searching for a hidden pass. The power of Ulmo in the Vale of Sirion also helped keep it secret. A law was set down that any stranger who might find their way to the city was not to leave, and no one but the people living there were to know its whereabouts. Within the mountain perimeter, all that was fair in elven culture was preserved, with reverence.