So my personal dream base setup would be on an island planet. I love the idea of building underwater stuff, exploring the deep oceans and whatnot. I havent gotten to the point in the base quests to GET to underwater building but I am working on it.

However, I am not sure exactly how building underwater works? I have seen that there appear to be unique base rooms and prefabs for underwater but do you just swim down there and start laying stuff down? Does the game know not to flood it?

And for that matter, can you dig out and build under ground areas as well? Does the terrain come back in (I have heard horror stories of this)

I am fairly new to the whole base building thing so I am just trying to understand it, is all! Any help would be most appreciated.