This is all actually doable if you don't mess with physics. Large physics objects just plain fall apart if you stare at them too hard, and explode spectacularly when you cross a sim boundary. One of my favorite experiences was crossing a line near a sandbox with an otherwise very stable structure, which caused it to pop like a soap bubble and rain down upon a nearby crowded orientation area. This was awesome, but inconvenient.
First: This is bad city planning.
Second: Immediate and exceptionally rude interrogation of the victim of such a bug by a GM is not class.
Third: Expressing incredulity when the bug is explained to you is just... wow. This is probably the single most well known and easily reproducible fuckup in the whole game and not only are your GMs ignorant of it, but immediately toggling their "yell and threaten" mode when it happens? I was actually hoping to get my account shut down over this- it would have made an excellent point in an article I was working on. The GM in question underwent a rapid change in tone, however. Such that I can only gather that someone more knowledgeable leaned in and told them that yes, you're harassing users because our game is broken, retard.
Anyway, if you want a great-big-flying-castle on a huge chunk of land, I have one of those. Fills up about a third of a sim. Very nearly finished, and actually 8-bit textured. Was thinking about going for a Mario-64 castle theme, sort of, but it could be tweaked pretty easy. Looks cool, and uses a script that has fuckall to do with physics. All the bits just check their relative positions against a single central prim, compare them against what their distances -should- be, and move themselves to it every few ticks. Not only is this limitless in size up to the point where the server will crash, it isn't prone to exploding and will pass through objects, precluding the possibility of getting the whole damn structure hung up on some little 1x1x1 piece of floatsam that someone accidentally teleported into the high atmosphere three years ago. Bonus: It has this property without being set phantom, so it's still actually solid and can be wandered around in/on while it's in motion. Somewhat less cool: it looks fucking weird if it moves at any pace faster than a dead snail nailed to a board. Which doesn't really bother me.
If they've changed the rules it may have issues with lost-and-founding when passing over some plots, but I'm unsure. But then, most anything will do this if it's not being worn or ridden, and this thing actually may not.
... dude, I'm going to have to attach it to my head.
