Building destroyers

Building destroyers are creatures that will actively seek out various furnishings, workshops and other buildings and topple or destroy them. They come in two varieties, the first being annoying, and the second dangerous. Most buildings will be "toppled" (deconstructed), leaving the building material or furniture unbuilt but otherwise unharmed, however doors, hatch covers, and floodgates will be damaged until destroyed, not deconstructed. They can destroy most furniture and buildings from a lower z-level when a valid path exists to that furniture, though locked hatches and closed grates are safe as long as no alternative paths exist.

Artifact quality furniture can never be damaged or destroyed, but some kinds of artifact furniture will be deconstructed by a building destroyer, given enough time, e.g. statues.

Level 1 creatures will go after statues, windows, archery targets, slabs, wooden doors, and wooden hatches.

Level 2 creatures will actively seek out all buildings and destroy them. The only buildings that will be spared by a building destroyer are wells, bridges, roads, traps (including levers and track stops), animal traps, chains, cages, stockpiles, and upright weapons. Constructions (walls, staircase, floors, etc.) are also safe, since they're processed the same way as natural terrain for most situations.