The stone labyrinths were there along with the mystic creatures that were there before Laanx and Talad arrived. Noone that we know of, built it, but they weren\'t made by nature.
The reason you can\'t just dig a hole into the wall and then fall out of Yliakum is 1) because the walls are very thick, and 2) because the upper level walls go straight into the ground, not into the emptyness of a big cave, and the reason the light reaches all levels is because the levels don\'t shadow out eachother. Like this:

Behold my great illustration. Anyway, the round thing connecting the two sides is supposed to show that the stalagtite is round, and the levels are all the way around, and not just on both sides, and since the cave is connected to the first level, you don\'t fall off by going into it, as it goes through the ground itself.
The reason why Yliakum isn\'t flooded is like I drew on the map. It\'s got a big hole in the bottom where the water runs out, but it does have tides so sometimes the water covers the 7th level entirely, and other times it doesn\'t.
And the reason that the world keeps having water is because the world is round, so the water runs out on the bottom of it and then moves up to the top and starts falling down again.
