Possible hint at where Labyrinthos is located.

[GoldStarz]

I think Labyrinthos is actually the space ship in the title card. It is located under Old Sharlayan and is the main reason for their reluctance to join in fighting the End Days as it is their escape from the star. My main reasoning for this is the music in the trailer when Old Sharlayan is shown. Here is the believed lyrics in one of the other threads:

Of Song of Hope, She Dances on the Wind,
Higher! Oh, Higher!
E've our foes endure
Everything for now is strong.
Standing tall in the dark till we carry on.
On Wings of Hope, You rise up through the Night,
Higher! Oh, Higher!
Carrying a song, may you fall into our hearts.
That its chorus might ring for all!

The chorus in the song has a lot references to flying or rising higher. I know it is pure speculation, but it's kind of how I'm putting the story together from what they have shown so far.

I really like this theory! It also would make the New Year's Poem make a ton of sense if they've been planning this long-term.

Our Progeny may never know
Wherefore we look unto the sky,
Nor why we dig for truths below;
We bear their scorn or watch them die.

If we take this theory into account it's essentially "We can't tell our people that we're building a spaceship underneath Sharlayan to prepare for the end of the world or we'd all die."

Also in addition to the artificial sun, we saw a dungeon in the showcase that seems to be simulating various seasons and also had some Sharlayan architecture.