The Andrean empire has been around for at least a thousand year which is long enough for some buildings to be ancient especially closet to the capitol. But just a few years ago on the frontier, a giant tower just appeared out of thin air. The rumors around its origin range from a random wizard wanting to build it to it being a potential portal to the nine hells to it being a lab for a superweapon.

I think this is an incredible starting point :) Try adding more factors relating to the relationship of the tower's appearance to the locale around it.

Try asking yourself;

-Why hasn't the tower been explored as of yet? If it has, what has been discovered out of it?
-What gossip is spreading surrounding the tower? What might have given the ideas behind these points of interest?
-What triggered this event? Why here and why now? Who had constructed this?
-If creatures are in the tower, why have they not come out yet? Are they protecting something? Are they magically forced to stay in?

I also noticed you cared for the age of the Empire that you are in. Perhaps consider whereabouts the tower is and how recently this area has been civilized. If the empire that now belongs to humans was founded on the throne of a giant then perhaps the Old City areas might be constructed appropriate to that type of peoples. If this reflects the area the tower appeared in, then it might follow suite and might even belong to a being that would have existed then?

Quote from DrinkableTrees >>

Try asking yourself;

...

 
Of course, these specific inquiries might not concern you. What I'm trying to suggest is unravel the ball of plot yarn you made and thread a story to explore out of it :D

Thanks already have a couple of first-tier quests planned really need to work on the lore