Darlings, I had to share this simple portal effect made with Ikea mirrors and rope lighting.
Links to the instructions can be found here. Of course, people walking in front of the mirrors will disrupt the illusion, so consider using the effect in an area where it can be placed high up, at an angle, or otherwise outside the general flow of traffic for your event. This effect would also be enhanced tremendously with a fog machine. Happy haunting, darlings, and do let me know if you give this one a try.