I want to create something like the first row of pictures here:
https://www.google.com/search?q=povray+cave&espv=2&biw=1838&bih=995&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjk6-TN7fPKAhVW22MKHTxUCdgQ_AUIBigB#tbm=isch&q=cave+entrance+model
It can be an entirely natural formation and not man-made.
What would be a good way to go about doing it?
Mike
