So after looking at it on some graph paper,
I figured out a procedure for making these mammoth terraces.
They will be the perfect breeding grounds for a new sort of plant I hope to implement.
In the first picture, we see a huge tower grid in the distance,
and a flat grid running over the top of a lake.
In the second picture, I found the coolest setup,
with an abandoned building sitting next to a huge complex,
which features a round plate sticking out of one side.
Nearer to the camera, you can see yet another grid, with a river behind it.
When I started the map, the water was pouring through the grid.
It was pretty sweet.
Also, water CAN affect the purple material somewhat,
slowly morphing and shifting its blocks.
Being mostly hollow, and having clean vertical shafts,
these offer no protection from the sky unmodified.
I'm going to add in a spherical version
before I move onto the next land feature.
EDIT:
Terraces have a one in five chance of filling in with land.
I've used one of the crystal abilities to rip a hole into the side of this one.
(After cheating myself to one thousand crystals)
EDIT 2:
I'm going to add in the ability to punch out the ceiling.
That way you can finally mine upwards, making these filled terraces much more fun.
Oh, and when I said water can slowly morph these things, this is what I meant: