Pictures with figures. The doors are 'split' large door for big creatures with a small door in it for smaller creatures. They are designed for the burrows figures which are based on 28mm scale.
As for the 'grey board' its card board nothing special - just like the backing board on sketch pads and stiffened envelopes. All the curves are easy if you score them, as said in the instructions. This 'deepens' the etched cut a little and relieves the stress in the card. These were all painted with a spray can for a base, emulsion over to add texture - in parts before gluing together. I still have plenty of paint in the can, and the same can was used for other stuff before these. Hope this answers some of the questions.