A prison with portals as walls.
The prisoner is brought into the room and when he is in this room then you close the portal with a lighter. If he wants to escape, he has to go through one of the portals, which will take him to the "other" world, where the other portal is. To guarantee that the prisoner does not escape you have to build the portal, CAUTION the portal must not be damaged just build 5 blocks high and 2 wide to be safe. This wall must be built around the whole portal and 2 blocks away from the portal.
This is the room in the Nether World. It must be built from two sides.
On the outside.
Instructions:Simply build 4 portals to a quadrangle and in the Nehterwelt the portal with stones to build. !!! The portal must still function !!!
Write me in the comments what you think of my idea. :) :)