You mean cover only the top layer so that everytime you run by it makes the nearby cave noise? You got it boss!

Fine, but since there isn’t enough dirt to fill it in I’m going to make a bunch of floating trees and fill it with wood :)

I myself like using a mod so that it automatically repairs itself

I like to keep one valley not patched so it looks like place where many battles took place

/gamerule mobGriefing false

Or embrace the hole and make it a perimeter

But leaving it alone adds environmental story telling for future explorers.

Or you can make it a little pond.

/set gamemode 0

FTB Chunks user: you have no power here.