This is a cute way to transform a cardboard box into an old-fashioned stone fireplace. I am not very good at taking pictures while I go but I think you will be able to figure out how I did this if you look at the back of the fireplace. I took one half of a small gift box and drew a square where the hearth would go. Using scissors and an exacto knife I removed it. Then I used brown paint to paint the outside of the box and enough of the inside so that the white would not show. I used two coats of brown acrylic paint.
Next I located tiny pebbles. An aquarium store would be good if you don't have a natural source. In our case, my children stole a bunch from the neighbor's driveway. (It was slated for repavement soon after.) They are varigated in color and size so look very realistic, I believe. We glued them onto the box using Tacky Glue. Initially I used Gorilla Glue but this was a mistake. It foams up when it dries. Tacky Glue holds the pebbles on perfectly well and does not show. I covered the entire front of the fireplace and the sides. On top I just lay a thin line of pebbles so that there would be a flat surface to hold knick knacks.
I made a candlestick out of half of a birthday candle glued onto a washer. I burned a bit of the candle down so that it would look more realistic. The vase is an old dollhouse vase I had when I was young with some sprigs of dried lavender.