A crazy way to have underground land?

What if you could stack sims and also invert the land mapping so the ground became the roof for the cavern then use a megaprim floor, then you could make a hole in the land between the upper and lower as the entry.

Of course being able to have terrain on the floor too would be even better but the 4096m gap might be a bit big. Can you terrain map that high?

Perhaps just using mega sculpty or land meshes would be the go instead in an existing sim.

Absolute limit for terrain mapping is from zero to 510 Meters.

It's much easier simply to make the caverns in a skybox, and teleport there from their entrance