Doors are one of the most versatile home items to work with and upcycle. They're basically just a set of solid-wood boards that can be repurposed for just about anything. However, turning them into headboards is one of the most popular DIY projects out there. All you need is a drill and you're pretty much finished. You just take the door, drill it to the wall using screws, and you have a new headboard.
Of course, you could go even further and attach the door to your bed frame or add a fresh coat of paint. Adjustments are also easy to make and only require a couple of simple cuts to make them proportional to your bed's size.