Getting into the Backrooms is a one-way trip. Prepare before you do it.
Before You Cross Over
1. Accept that your inventory is gone. Everything you carry is cleared when you arrive, so there is no point stockpiling gear for the trip. Store anything valuable in chests, or simply use it up.
2. Accept that you cannot come back. You cannot return to the Overworld once you enter. If you want to keep your normal base, consider starting the Backrooms run in a separate world or save.
3. Grab a falling block. Sand, gravel or any other block that falls with gravity will work.
Triggering the Transfer
1. Find or dig a spot where a dropped block will land directly on your head. A narrow one-block-wide space works well because the block cannot slide away.
2. Place sand or gravel directly above your head so it drops onto you.
3. Stay put and let yourself suffocate. Do not dig out or jump clear.
4. You will wake up inside Level 0, the classic yellow-wallpaper rooms with damp carpet, carrying nothing.
First Seconds Inside
Don't panic-run. Look around, note the wallpaper corridors, and start searching nearby rooms right away. Food and sanity management begin immediately. A slow, methodical sweep of the first few rooms is better than sprinting blindly into the maze.