Well, four entries have certainly been had! So here goes the judgy mudging:
A Winrar is You!

hectic was the only one who I think really captured the idea of a lost civilization. It's a crumbling castle with overgrowing plains, which is about as lost civilization as you can get. The only thing I would have done to make it better would be to have vines and such inside the cobbles of the castle, but otherwise it looks pretty fine and dandy.
Running Up

Even though I'm not super keen on fanart, you did a good job with the bleeding (likely due to the high humidity of a beach) letters and the beach itself. The keyblade is a little awkward in the sand, but I think it works pretty well anyway. The reason why this didn't get first was because it didn't really give me thoughts on any lost civilization- I'd reckon it's because I haven't played any of the Kingdom Hearts games.
Simplicity Award

This almost beat hectic, if but the castle isn't near crumbly enough or devastated enough to be considered a lost part of a civilization. Even so, it has a certain charm of simplicity that only basic shapes can provide.
Sin City

I have a weak point for cityscapes, because they make my brain and heart get all thumpy and flustered. Sadly though, the theme was a Lost kingdom, and less an already found kingdom. Even so, charming as always.
The new theme!
I like fire. A lot. Some people would tell me that I'm immature because of it, others would associate with me and say "Yeah, I like fire a lot too". Even more, people would call me a lunatic with the amount of myself I see in the dancing flames and would tell me that I need to see a mental doctor as soon as was physically possible. I set those people on fire.
So the new theme will be water. Just kidding, it's fire. Just kidding again! It's both. You can do either Fire, Water, or if you want BONUS points when judging comes around, Fire & Water.
I think I'll give this two weeks, but if I have the minimum 4 entries by the end of next Tuesday, I'll do the judging then. :) Happy Tuesday everyone, let's see some good stuff!