DOOR is made by splicing DIRT and CAVE BACKGROUND. DOOR belongs to doors category. This thing grows like weed... NOT that weed you silly. You get experiance points for breaking DOOR. Hitting it will break it but you need to count the hits yourself. By default you should get at least 1 seed back. Profiting with this might be questionable. Massproducing DOOR can be tricky. You will find out after you have harvested a few.