The second card I made during my "pop up card" phase is this one. Not sure if this is technically a pop up card, but you can see that when you open up the square card, it'll stand up. Contrary to the Pop Up Stack of Gifts card, I decorated all 3 interior faces. To keep it tightly closed, I again used ribbon.
Outside of the card, tied with a ribbon to prevent popping up.
What the card looks like when it's opened up.