Here is a link to the tutorial: https://www.instructables.com/id/Valentines-Day-Portal-Companion-Cube-Pop-Up-Card/
It's a pop-up card for Valentine's Day that I put together myself. For your valentine who would get a portal gaming reference, that is. If you don't think that's going to fly, then you probably want a more traditional card.
The tutorial is done in real time so that you know exactly how to make it.