About 7 years ago, I was playing Minecraft at a friends place and stumbled across this open plain near the woods with hundreds of ender portal frames arranged in a maze-like manner. It was extremely creepy and I'm fairly sure we were playing vanilla survival on a world that hadn't previously been touched. To this day we still don't know what the hell it was. If anyone else knows about something like this or has ran into something similar please let me know because it has bothering me for years.
And now you've discovered that your friend lies to you like a cheap rug. What you saw does not exist in vanilla Minecraft at all, and I haven't heard of anything like this in the modded sphere. Your friend either built it himself and tricked you, or downloaded a schematic/custom map and tricked you. Either way, you got played hard.
Then again, perhaps you have a big brother/sister/whatever who constantly messes with you and/or your friends...same result, now with more victims.