Yeah, as said above you could use the cardboard for just about anything. If you just cut it up into sections you can use it for all sorts of scenery projects including buildings, roads rivers, hills... the list goes on.
The most obvious use for the boxes is as the base shape for a building. Appropriate cutting can turn them into a ruin, or you could use them in tiers to make some sort of huge tower or plinth for a statue.
The card rolls could be used to make tunnels, pipes or chimneys. Alternatively you could cut them in half and use them as some sort of curved roof over a walkway or something similar.
Just let your imagination run riot
Rich.