How to make a floating island in unity?

I am making a game with islands, I am using unity terrain for that. The problem is, I don't want regular I want floating ones. The problem with Unity terrain is that you can only create islands like this:

But I want something like this:

I was thinking about creating another terrain and then flipping it upside down, but the problem there would be that the alignment of the two terrains would not be the same.

Does anyone know a solution to this problem?

Thanks in advance Emiel

The way I would do it is to create the shape of your floating island, use the paint holes brush to remove the leftover outer areas you don't want to use for your island, duplicate the terrain and use the brushes on the duplicated one to look like an underside, then flip it (I'd probably convert it to a normal mesh if I did it). Then simply cover up the edges with rocks or other things to hide that seam where the two terrains meet.

This way, at least the top of the floating island remains a usable Unity terrain, just in case you intend to use terrain shaders on it.