Hoping to make your life's design a bit more dynamic!

Does it have something to do the sunken city (forget it's name). I remember a secret room that's SUPER hard to find being there somewhere. Sorry I can't be of much help. It's been a year since I tested, and I've all but forgotten.

Do you mean the last boss place? Gyab Far's Base?

Nope. The town north of shell dorado that sank.

yep.. lamille, that's where i found the key, but i have been all over the sunken town to look
for where i use the key but not found anywhere.

Okay, do you remember going through dungeons between Sandside and somewhere? I believe you could see parts of that system that were inaccessible. Later, you get one of the two subs and go either deep or into the abyss - somewhere high or low, not sure, but maybe near Sandside underwater. I believe you blow a new torpedo entrance, and you get into an area where I believe you find the Ancient Key (Is that how you got it?) Anyway (and I might be off with this), the Ancient Key may unlock a door somewhere that reaches that inaccessible area near Sandside.

I found the key down the well in Lamille, before the city is flooded and put under water, iv'e checked after flood and before flood, you can get the key whenever.. as long as you have Helper: Myan. This key is a mystery to me, it HAS to be used for something, doubt they'd put a key in THIS game for it not to be used.. unless they just didn't finish programming the game completely, which i highly doubt. I'm thinking maybe there's some hidden dungeon to be unlocked :O that'd be awesome, that maybe has the rest of Poyon's skills in it to get :O *falls off into a daydream* i can only but wish.