To make the card, I used the same method that you would use to make a traditional box card. The difference is that I cut out the front of the box, replacing it with a transparency sheet, then used brown cardstock, to make the "middle insert" piece. Then it was as easy as stamping my little fish friends, coloring them, an setting the scene. To put the "box card" in an envelope, you just press it down, and it folds over, just like a traditional box card. I will admit, I tried to make an A2 size card at first, but all the pieces just didn't fit very well, so I increased the size. When flattened, this card fits in to a 5X7 envelope perfectly, though it does have a little bulk to it. You can see the thickness of the project, in the images below.
I hope you enjoy and that this inspires you to create something fantastic!
Lawn Fawn (stamps and Dies): Critters in the Sea, Fintastic Friends, and Life is Good
Paper: Recollections Cardstock & Christmas/Noel 6X6 Pattern Paper Pack by American Crafts
Spectrum Noir Markers
Tim Holtz Distress Inks: Tumbled Glass & Broken China (for the water back ground)
Other: Foam Tape & Transparency Sheets
My "Best Fishes" box/aquarium card was chosen as a Party Pick on the PDE Linky Party Blog.