It's beginning to look a lot like Christmas, especially now that my apartment has a fireplace!

All you need is a large cardboard box, a box cutter, scissors, tape, , hot glue, brown wrapping paper, and a Sharpie.

Step 1: Tape Up the Corners of a Large Cardboard Box.

I used duct tape to secure the corners of a large cardboard box so that it would stand up on its flaps.

Step 2: Cut Out a Rectangle to Leave Space for the "fire."

Use a box cutter to cut out a rectangle from one side of the box. I found it easiest to do so on carpeted floor (it didn't hurt the carpet). To give you an idea of the proportions, my rectangle is seven inches out from the edges.

Step 3: Cut the Box in Half.

Since the box is quite large, and I wanted my mantel to only stick out about a foot form the wall, I used the box cutter to cut the box in half, using the flaps as a guide.

Step 4: Make Extensions to Your Box If Necessary.

Depending on how big your box was to begin with, you may want to make it taller or wider to get it to a good fireplace size. On my box, I cut off the flaps on the half I didn't use and hot-glued them to the bottoms of my fireplace, overlapping by a couple inches. This brought the total height up to four feet. Since it was now so tall, I decided to widen it as well by cutting the horizontal piece in half and inserting another piece of cardboard. This insert was reinforced with more tape and another cardboard piece underneath.

Step 5: Decorate Your Fireplace!

I cut out brown wrapping paper (~$6 at Staples, but I barely used a fraction of the roll) and wrapped the front of the fireplace. I wrapped the middle horizontal piece first, then the sides, and finally the extensions at the bottom. All of it was taped down with brown paper tape. I tried to trim the inside corners to get a mitered corner look.

I looked up Art Nouveau designs and used pencil to sketch my "carvings" onto my fireplace, then traced over it in Sharpie. This website also has a lot of line art examples of different fireplace looks, some of which are easier to reproduce than others:
http://www.stevensons-of-norwich.co.uk/products/paginate_by/all/

Step 6: Set Up Your Fireplace.

I placed my fireplace on a wall so that one of the vertical pieces covered up a socket. That way I could set up my lights for the "fire" in the middle and then plug it in and have the plug be hidden.

My fire is a string of Christmas lights looped around an upturned ceramic bowl with a pillar candle in the middle, all set up on a box that I draped with some fabric. I put more fabric on the top of the fireplace and set up Christmas cards and other lightweight decorations. For extra support, I placed a couple of pushpins in the wall under the horizontal piece.