Many homes and apartments come equipped with what was once a fireplace, but, for one reason or another, it has been closed off by the landlords, leaving behind a hole in the wall and a mantle. While decorating a working fireplace is a fairly straightforward endeavor, making one that no longer works a part of your design scheme can be somewhat of a challenge.
In the end, the way that you deal with your fireplace will probably have to do with its overall structural integrity. If it's in good enough shape that you would want to look at it daily, you can use the mantle as a display shelf and even hold something beautiful within. Often, homeowners will store decorative logs in a former fireplace as a nod to its original function, though there are many other uses that can be good as well—books, magazines and even art all work well in this space.
But in some cases, the fireplace was boarded up so that the area where a fire used to be contained, as well as any decoration that might have surrounded it, is covered. In a situation like this, it can be a little harder to know what to do, as it's really not all that pretty.
Rather than try to make this odd part of your wall look better, you might have more luck covering it entirely. Leave the mantel open and pick a set of solid silk drapes to hang beneath. This will give your boarded up fireplace a better context, turning it into a nice background for an accent chair or similar solution.
Just because it no longer works doesn't mean the fireplace in your home can't still be the center of the decor.