Can't believe I'm having this problem, but I keep trying to place a cave into the world, and I see nothing when I enter the game. I know the CK is working because I can see other changes like removed objects and what not. I must be missing a step.. anyone know what that is?

Make sure that Skyrim is loading your plugin. When you run the game through Steam, Click "Data Files" from the launcher. You should see your plugin appear in this list. Ensure it's enabled, indicated by a checkbox. When you've confirmed this, click OK, then "Play Game".

Thx for the fast response.
Yup, it's checked off in Data files. I can actually see other changes, say if I delete a mountain, but for some reason the cave entrance I drag into the world is just not there... hmm.

Ah - It sounds like you may have built something that's being covered up by the LOD landscape. When you're in the game, try entering the console with tilde (~) and typing the command TLL, then hitting enter. If my suspicions are accurate, you'll see your cave.

LOD stands for "level of detail". It's a common game dev term for any piece of art which is simplified when far away, therefore making it easier for the computer to draw additional stuff. As you can imagine, this is a critical system for Skyrim. At any given time, the area immediately surrounding the player is drawn at full detail, but the environment beyond is using LOD.

Generating new world LOD is no easy task - so in your case, I'd recommend building up instead of digging down. It's still possible to get the feel of going down into an entrance, of course - it usually requires some creative building, though. Luckily you can preview LOD landscape in-editor now. Right-click anywhere in the Render Window viewport and choose "render window properties", then click the LOD tab. Check the "Enable Landscape LOD" button and you should be good to go.

Good luck!

Glad I asked this question. Thanks for the LOD info, I definitely was on track to run into that problem. Sry though, I should have been more specific. I've been dragging the object "RockCaveEntrance01" from the object window into render window. When I do, I do see the cave entrance in all its glory in the render window, but when I load up the game, I see nothing of the cave in the actual game world.

I'll try it again, it may be one of those things where it just doesnt work one moment, and it works the next and your like, "hmmkay, whatever."

EDIT: Okay, I placed the cave in a different spot and i see it in game now... Then I went back and noticed that before I had been placing the cave in an area that was inside some orange framed box... I have no idea what that frame is, or if it was the reason my cave object wouldnt show up but..... hmmmkay, whatever. Thanks again.

I had the exact same issue, all i did was tick the box "is full lod" and it showed up fine in game.

I had a similar issue with a builiding, it turned out out there was a small red box (looks like the Oblivion version of the teleport marker) and it had a yellow line connected to it that was apparently connected to somthing else (though I could not see it) and that line crossed over my building. Getting rid of that reference seemed to have solved my problem.I guess it just deletes any object that conflicts with effects or creatures or whatever.