I have a project where I may have to make surfaces like a cave wall of rocks, etc. I know I can make random curves and loft. with history on I can adjust the curve points to randomize the surface beyond the original curves. I’m wondering is SubD migh be another option. I gave up on SubD but It seems it might be simple enough for this purpose. Thoughts, suggestions, recommendations?
does it have to be NURBS? if not, then a sculpting program like Zbrush may be a better choice for work like this.
If that is not an option, do you have an image of what you are aiming for? Subd and some heavy duty displacement mapping may get your there.
I’m modeling a mausoleum set with a door into a cave. Does not have to match anything really, just needs to be undulating so the construction people know it’s not flat wall. I can just make a note, but would like to be a little visual in the model.
Rhino is the program I have. Doesn’t have to be NURBS, but it’s what I can do using loft and push-pull points.I have no idea what displacement mapping is?
I do have Blender but have never really used it. So though I think that could work, importing the wall plan, learning to sculpt, and then returning the finished elements to Rhino is probably more that I can do in the time I have. I probably could sculpt it in full scale quicker. 
I use a SubD base with a displacement map for stuff like this. Modeled and drafter a few caves that way. Gives you control of the massing while giving you the cave texture and feel. And it’s quicker than sculpting in ZBrush or Blender. If you need to ‘bake’ the mesh, you can extract the render mesh and that works for most purposes.
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Thanks for the response David. I haven’t used SubD for a while, but might be able to get back into it. I’m not sure if I’ll have the time to re-lean though. I don’t know what a “displacement map” is or how to create and use one. Something else to learn if I can figure out where to start.
check out this awesome video Brian James did for displacement tips-
Thanks Kyle. I watched the video and fiddled a bit, but it will take me a while to get a handle on it. Like knowing what to expect so I can choose the right images/texture, etc., to get what I need. At present, I think SubD is starting to give me enough. However, I need my SubD objects to end up with straight corners put that does not seem possible. I tried add crease but that did not work.
Perhaps try creasing the vertex
that corner will have a vertex on the corner edge which is probably made of 2 edges.
Akash
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As Akash noted above, crease the corner vertexes for a sharp corner.
Yep. Just tried it. Gives what I need. Thanks.