When I was young I had an impressive collection of wargames scenery, including several hills, bunkers, buildings, woods and a huge shrine with a 25cm-diameter magic circle, 10cm pillars all mounted on a big hill... and my collection of scenery took up half the storage space I had.
Then Games Workshop released Necromunda, which came with some innovative scenery. The setting of the game was cramped and claustrophobic, so the typical card ruins found in contemporary games would be rather pathetic; instead the game came with a set of plastic bulkheads, with card-width slots around three edges on both sides. The bulkheads themselves link together in neat stacks, and a variety of neatly-shaped card building pieces affixed to them in different ways to create a multi-leveled and relatively dense game. The best bit was how this dense battlefield was constructed entirely from flat bits of card and plastic bulkheads - I have all my Necromunda scenery in an A4 box 8cm or so deep, but it folds out and fits together to cover a square metre or so of gaming table.
It's a nice ideal... and the bulkheads are just asking for more designs, so I came to create another set of cardboard pieces to make another flatpack item - this time a fortress.