Dunno if this has been mentioned before, but the Crystal Tower was teased in 1.0.

If you talk to Erik (MNK quest NPC) and ask about Silvertear Falls (2nd page), he'll say, among other things:

Quote Originally Posted by Erik
Do you not see? <sigh> Of course you don't... It could only be the lost tomb of Xandes─the first emperor of Allag of whom I spoke mere moments ago. But wait, there it more to tell! You see, it is impossible that a normal building, however large, could release so much ethereal energy. An immense crystal on the other hand─that most certainly could. Putting these observations together, I had no choice but to conclude that the ancients' seemingly fanciful references to the tomb being wrought of crystal were not so fanciful after all!

And that is the history of Silvertear Falls─or as much as I am willing to expose that meager mind of yours to in one telling. <sigh> If only there were some way to access this crystal tower beneath the surface... It would prove my theory and be the discovery of the century!