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.