: Yeah, I'm guessing they're able to add terrain-like objects to the existing
: terrain and that these objects adapt to the existing terrain. Malleable
: was too strong a word there, I doubt you can "dig" into any of
: this terrain.

and lay tunnels to them.

These structures could have inner and outer walls so they could be half in and half out of the ground. If they are completely buried then the outer walls could be removed by the engine to save resources. Openings are just door frames that you place in the solid walls and they become entrances. You can place ledges, ramps, roads and tunnels up to them.

I'd also have a selection of cave interiors to place in cliffs and under ground.

Maybe we need a canyon digger and we could remake AotCR.