I own nothing.
No one knows about the dream—not even Finrod, who had fallen into deep slumber on the stream bank beside him, and had woken troubled enough that Turgon suspects that he had a dream of his own—until Turgon tells Aredhel, years later. They're well-settled in Vinyamar, have put so much effort into the making of this city and the creation of a new life, and he's swallowed on his fears, his wants, his memory of that dream. But it's always been in the back of his mind, lingering, that day, when a voice more akin to tide than tone, told him of a chance for safety and a place where he could take his people to ensure it.
"So that's where you went last month?" Aredhel asks once he's finished with his tale. They're in the library where Turgon found her, alone; everyone else has been ordered out. It's rare enough to find Aredhel indoors, let alone in the library, and Turgon's relieved enough to have found her somewhere he can ensure privacy that he doesn't suggest that they remove to some smaller room. "To this vale in the Echoriath?"
He nods choppily. "Yes, that was where Lord Ulmo said to…" Turgon trails off as, at last, it occurs to him just how absurd what he's saying sounds. He looks over at Aredhel, who is leaning against the wall with her arms folded across her chest, giving him a scrutinizing look. "I… I can understand if you think that I am joking, sister. Or if you think I'm lying."
To his undying relief, she shakes her head and answers almost immediately. "No, I don't think you're joking. Or lying. You've never been much of one for joking, Turukáno."
"Oh, thank you," Turgon mutter sourly.
"You've never been much of one for lying, either," Aredhel goes on, as though he never interrupted her. She smirks slightly. "And when you do lie, your lies aren't nearly this creative."
"Thank you once again, Irissë, for that vote of confidence."
Her observations go thoroughly unappreciated. But it does truly leave Turgon relieved, that she believes him so readily. If Aredhel had not believed him, Turgon does not see how he would have gotten anyone else to.
After that, he sets his plans in motion. Aredhel and Idril and everyone else involved are sworn to secrecy, even against their own kin outside of Nevrast. Plans are drawn up for a city hidden in a secluded vale, deep in the Encircling Mountains, where no one, neither Morgoth's creatures nor the Quendi, will find them. This was Lord Ulmo's boon to the Noldor, given despite their slaughter of the Falmari. It is likely to be the only boon they shall be given, and any boon Turgon can claim on behalf of his people, he will take.
The memory of the Grinding Ice and what it took still clings all too fast to his mind. The memory of what they lost in those early years in the Lammoth and Mithrim, when they were clinging to survival, weathering attack after attack, that stays fresh and too-sharp in his mind as well. The sign given to Turgon need not have been something so concrete as the dream Lord Ulmo sent him. He would have taken even the smallest hint. If there was even the smallest chance of ensuring safety for his people, he would have taken it.
They make the plans in secret, drawing up the city, determining how best to move the people into the Vale, and do all of this in such a way that will prevent discovery. "I really don't know much about architecture," Aredhel mutters from time to time, rubbing her forehead and casting a longing gaze outside from time to time. Turgon doesn't either (and he understands even less at what point she decided to come with him and why), but he doesn't say as much.
There are times, intermittent times, when Turgon feels a pang of conscience, for his father, for his older brother, for Finrod and his brothers. But he quells it. They make their plans in secret, as they must.
Turgon looks at the plans they've drawn up for his hidden city, and he feels the future resting in the palms of his hands. All he has to do is close his fingers and claim it.
Turukáno—Turgon
Irissë—Aredhel
Echoriath—the Encircling Mountains, the mountain range where the Vale of Tumladen and Gondolin is located
Quendi—Elves (singular: Quendë) (Quenya)
Falmari—those among the Teleri who completed the journey to Aman; the name is derived from the Quenya falma, '[crested] wave.'