You know why there is no atlantis after ver 10.0.0 ? cuz in version 10.0.0 and after, there is a line, that separates underworld from sea. but this line is easily exposed, and this line too far above like after maybe 200 blocks down you find the line seperating underworld, while atlantis is found only after like 300 blocks deep. This 'line' is the reason why we cannot find atlantis and other stuff. see screenshot 63. I don't know what that is, cuz I have not explored it completely. screenshot 64 is from other angle. thanks to Conboy, i got to know what screenshot 65 is. Here http://www.blockstory.net/forum/what-0, where conboy said about it. The reason why that forgotten temple had not completely generated is cuz it cannot generate in underworld ( the game will see the space after the line as underworld ) and so it will stop generating.
I am still not completely sure, but we need to get it fixed...
My best guess is its some kind of terrain generating glitch. I've never made the structures or the generator, so I can't say for certain...
I have seen these many times they happen when you are neer hell, so you see how the water stops, after that is hell and hell will cut off any building that spawns in it from up top.
I'll have to check this out myself. I've never seen anything like it, and I'd like to see more of this.