When I was about ten, I visited a nightclub for a party of some kind; an aunt or uncle’s birthday, I think. In the hallway into the main room was a large window into another universe. At least, that’s what it looked like to me at age ten. 
It was actually an infinity mirror: a regular mirror in the back, a string of lights around the edge, and then a two-way mirror in the front. The reflection of the lights bounces back and forth, and it feels like you’re peering into deep hole in the fabric of space.
It made such an impression on me that I’ve thought about it ever since, and finally decided to build one. It took about three hours construction time. I ordered LEDs ribbon lights and a two-way mirror film online, and picked up the rest locally. The two mirrors are held apart by a 1×4 wooden frame, and L shaped molding holds the mirrors onto the frame. The mirror and the glass are 24″ by 36″, and I went with that dimension because they were both available precut in that size.