A ruined portal is a naturally generated damaged nether portal, which spawns in both the Nether and the Overworld. It contains some decoration and a loot chest around it. - Minecraft Gamepedia
More Information: Click here to view the wiki
IMPORTANT: Print the second page (The one with the crying obsidian) 1 time, and then just print the third page (the one with a 2x1 obsidian block) 3 times.
Credits to: M16 who helped me by fixing the scaling errors in the design.
Also see my Mini Ruined Portal
How to Print?
1.Click on the papercraft design image.
2.Make sure it has not been resized by your browser (you might need to click the image again).
3.Print using your browser's Print function.