This game appears to originate on a Korean website some may recognize as the source of a particular comic that pops up every few months or so on sites like reddit. Unfortunately I don't speak Korean, so working off of the rough translation found here, I've tried to tease out a clearer version of the rules and instructions. It's unclear whether the Otherworld to which the elevator delivers you is the Shadowside referred to by FableForge in his various games and rituals, or whether it's something else; regardless as to what it may or may not be, however, as always-play at your own risk.
Players:
1 principal
Requirements:
1 building, at least 10 stories high, with an elevator. All three of these conditions must be met in order for the game to proceeds.
Instructions:
Venturing Out:
Enter your chosen building and get into the elevator on the first floor alone. Do not proceed if anyone else is in the elevator with you.
Press the button for the fourth floor.
When the elevator reaches the fourth floor, do not get out. Instead, remain in the elevator and press the button for the second floor.
When you reach the second floor, remain in the elevator and press the button for the sixth floor.
When you reach the sixth floor, remain in the elevator and press the button for the second floor.
When you reach the second floor, remain in the elevator and press the button for the tenth floor.
When you reach the tenth floor, remain in the elevator and press the button for the fifth floor.
When you reach the fifth floor, a young woman may enter the elevator. Do not look at her; do not speak to her. She is not what she seems.
Press the button for the first floor. If the elevator begins ascending to the tenth floor instead of descending to the first, you may proceed. If the elevator descends to the first floor, exit as soon as the doors open. Do not look back. Do not speak.
If you reach the tenth floor, you may either choose to get off the elevator or to stay on it. If you choose to get off, and if the woman entered the elevator on the fifth floor, she will ask you, "Where are you going?" Do NOT answer her. Do NOT look at her.
You will know whether you have arrived at the Otherworld by one indication, and one indication only: The only person present in it is you.
The Return Trip:
If you chose to stay on the elevator at the tenth floor:
Press the button for the first floor. If it doesn't work, keep pressing it until it finally does.
When the elevator reaches the first floor, exit as soon as the doors open. Do not look back. Do not speak.
If you choose to exit the elevator at the tenth floor:
You must use the same elevator to return as the one in which you arrived.
When you enter the elevator, press the buttons in the same order you did in steps 2 through 8 of Venturing Out. You should finish at the fifth floor.
When you reach the fifth floor, press the button for the first floor. The elevator will again begin to ascend to the tenth floor. Press any other floor's button to cancel the ascension. You MUST press the button you use to cancel the ascension BEFORE you reach the tenth floor.
After you reach the first floor, check your surroundings carefully. If anything seems off-even the smallest detail-do NOT exit the elevator. If you detect something wrong, repeat step 2 until your surroundings look as they should. Once you are confident you have returned to your own world, you may safely exit the elevator.
Additional Notes:
Should you reach the Otherworld, the floor onto which you will emerge will look almost identical to the one from your own world, save for two things: All the lights will be off, and the only thing you will be able to see from the windows is a red cross in the distance.
Some say that electronic devices-mobile phones, cameras, MP3 players, etc.-don't work in the Otherworld; others say they do.
Getting back to your own world may be more difficult than it seems: You may become disoriented and forget which elevator in which you arrived; the elevator may seem to get further and further away from you as you walk towards; and so on. Be vigilant, and keep your wits about you.
If at any point during the ritual you faint, pass out, or otherwise lose consciousness, you will likely wake up in your own home. However, be sure to carefully examine your surroundings upon waking-the "home" to which you have been returned may not be the one you left when you first set out to attempt this ritual.
Concerning the woman on the Fifth Floor:
DO NOT speak to her
DO NOT look at her
If you do, she may decide to keep you for her own.