In Chapter 1 of The Mimic on Roblox, the “basement” is reached after you progress through the school section and unlock the stairwell area that leads downward. The walkthrough notes that after you get the key, you open the door in the hallway and then go down the stairs to enter the next part of the chapter.

How to get there

  1. Enter the school through the back entrance.
  2. Explore the gym/pool area and collect the key from the shed area.
  3. Continue through the school hallway and open the needed classroom/door.
  4. Take the stairs down when the stairwell appears to reach the basement-like transition into Part II.

Helpful tip

If you’re stuck, the basement is not usually a hidden side room early on — it’s part of the main progression path, so you need to keep following the key- and-door sequence rather than searching randomly.

Very short version

Get the key, open the hallway door, then go downstairs.