Anyway, here is some references.
You found Ultima Weapon wielding a sword similar to Cloud's sword which is also called "Ultima weapon" at the bottom of DSRC.
You can draw a mysterious GF called "Eden" from it.
A sword is stationed to guard Eden.The Garden of Eden story recounts how God created Adam and Eve, commanded them not to eat from the Tree of Knowledge of Good and Evil, and how they were expelled from the garden after they disobeyed Him, having been tempted by a serpent, and ate the fruit. As part of the Expulsion, cherubim and a flaming sword were stationed at the entrance to the garden, in order to prevent man from returning and eating from the Tree of Life.
In FF VI, Atma Weapon came with a package of a sword and a monster.
In FFV II, Ultimate Weapon dropped a sword upon defeat.
In FF VIII, Ultima Weapon wield a sword.
So there is no telling that Ultima Weapon is the sword itself. It is the sword itself that is the "Ultima Weapon". Even if it's not, we know that a sword wielding monster guard Eden, which is close enough.
So the location of Eden might be sunken?And we happen to find it under the sea in FF VIII?Others point out that the world of Eden's time was destroyed during Noah's Flood and it is therefore impossible to place the Garden anywhere in post-flood geography. There is also an attempt to tie this with the mystical sunken land of Atlantis.
BTW, what is the main purposes of visiting DSRC? Personally, I find it as accquiring Eden since this the last and possible thing to do in DSRC. And most rewarding too.
So the whole ruins might be based on mythical references like what Square do with the other FF games.